A few things

1. http://like-a-stone-wall.webs.com/ is an excellent website, with some lovely pictures of a Boyne game which was fought earlier this year

2. Brownsing the pdfs on Internet Archive (an excellent pastime), I have some choice quotes regarding the period, with a vague theme of uniforms:

"the scene passing in the Irish camp... was highly characteristic of the people and the cause they advocated. 'Twas the dawn
of the Sabbath morning, and its advent was solemnized
by those religious observances, the preparations for which
had been made through the preceding night. And those
ceremonies being ended, the troops were drawn out in the
same order of battle in which they had, for the last two
days, been awaiting the arrival of the enemy. As they
stood in their mingled uniforms of red and green, with
colors advanced, and their old battle-flag, bearing the
emblem of an early civilization, and standing out above
the long line of tents that formed the background, they
made a most gallant show, which the import of the hour
and the associations of the day and place rendered deeply
solemn and impressive. "

From "The battle-fields of Ireland, from 1688 to 1691: including Limerick and Athlone, Aughrim and the Boyne" by John Boyle. Rather tantalising references to green uniforms and the mysterious 'emblem of an early civilization'

"It was three o'clock in the afternoon when the fire of
the enemy's cannon ceased along the whole line, and the
assaulting columns, in their v aricolored uniforms of buff,
blue, and scarlet, moved down to the intrenchments as
gayly as if on parade, and halted. The fire within the
town also ceased, and an ominous silence settled over the
scene, the combatants on each side, standing with bated
breath, and as motionless as statues. An unusual drought
prevailed, — not a drop of rain had fallen for three weeks ;*
the weather was intensely hot, and the sun threw a flood
of unobstructed light upon dome and spire, while the river
glided away through its autumnal foliage, as placid as if
peace had returned and war should revisit it no more.
Some time passed on, and suspense was becoming pain-
ful, when the signal : one ! two ! three ! pealed forth. The
British grenadiers were over the palisades in a twink-
ling, hurling their destructive missiles, and followed by
the Dutch Guards, while the cannon rang out again
along the whole front, excepting the point of assault."

As above. Mention of buff uniforms among a very evocative passage depicting the Siege of Limerick.

"There happened to be
a large accumulation of this grey cloth in the French
warehouses, for in the winter of the same year a quantity
sufficient for 20,000 uniforms was sent to Ireland. But
there is one point that lends a piquant interest to the busi-
ness of clothing the Mountcashell brigade. The Irish
troops clamoured for red coats, and Lord Mountcashell
received an assurance that when new uniforms had to be
provided they should be in red. It is curious to find these
poor Irish exiles, who had gone forth from their own land

because they had been persuaded that England was their
natural enemy, protesting that they would wear the English
national uniform and no other. Their flag also was the
English flag. It was St. George's Cross, with a lion in gold,
and above it a golden crown in the centre. No one thought
of the Green Flag or the Harp in those days ! "

From "The battle of the Boyne, together with an account based on French and other unpublished records of the war in Ireland" by Demetrius Charles de Kavanagh Boulger

"Each of the contending princes had some ad-
vantages over his rival. James, standing on the
defensive, behind intrenchments, with a river
before him, had the stronger position, but his
troups were inferior both in number and in
quality to those which were opposed to him.
He probably had thirty thousand men. About
a third part of this force consisted of excellent
French infantry and excellent Irish cavalry. But
the rest of his army was the scoff of all Europe.
The Irish dragoons were bad ; the Irish infantry
worse. It was said that their ordinary way of
fighting was to discharge their pieces once, and
then to run away bawling " Quarter " and
"Murder." Their inefficiency was, in that age,
commonly imputed, both by their enemies and
by their allies, to natural poltroonery. How
little grounds there was for such an imputa-
tion has since been signally proved by many
heroic achievements in every part of the globe.

It ought, indeed, even in the seventeenth cen-
tury, to have occurred to reasonable men, that
a race which furnished some of the best horse-
soldiers in the world would certainly, with judi-
cous training, furnish good foot-soldiers. But
the Irish foot-soldiers had not merely not been
well trained ; they had been elaborately ill
trained. The greatest of our generals repeatedly
and emphatically declared that even the admir-
able army which fought its way, under his com-
mand, from Torres Yedras to Toulouse, would,
if he had suffered it to contract habits of pil-
lage, have become, in a few weeks, unfit for
all military purposes. What, then, was likely to
be the character of the troops who, from the day
on which they enlisted, were not merely per-
mitted, but invited to supply the deficiencies of
pay by marauding? They were, as might have
been expected, a mere mob — furious indeed, and
clamorous in their zeal for the cause which
they had espoused, but incapable of opposing a
steadfast resistance to a well-ordered force. In
truth, all that the discipline, if it is to be so
called, of James's army had done for the Celtic
kerne had been to debase and enervate him.
After eighteen months of nominal soldiership he
was positively farther from being a soldier than
on the day on which he quitted his hovel for
the camp.

William had under his command nearly thirty-
six thousand men, born in many lands and speak-
ing many tongues. Scarcely one Protestant
Church, scarcely one Protestant nation, was un-
represented in the army which a strange series
of events had brought to fight for the Protestant
religion in the remotest island of the West.
About half the troops were natives of England.
Ormond was there with the Life Guards,
and Oxford with the Blues. Sir John Lanier,
an officer who had acquired military experi-
ence on the Continent, and whose prudence
was held in high esteem, was at the head of the
Queen's Regiment of Horse, now the First Dra-
goon Guards. There were Beamont's foot, who
had, in defiance of the mandate of James, re-
fused to admit papists among them, and Hast-
ings's foot, who had, on the disastrous day of Kil-
liecrankie, maintained the military reputation of
the Saxon race. There were two Tangier battal-
ions, hitherto known only by deeds of violence and
rapine, but destined to begin, on the following
morning, a long career of glory. The Scotch
Guards marched under the command of their
countryman James Douglas. Two fine British
regiments which had been in the service of the
States-General, and had often looked death in
the face under William's leading, followed him
in this campaign, not only as their general, but
as their native king. They now rank as the fifth
and sixth of the line. The former was led by
an officer who had no skill in the higher parts
of military science, but whom the whole army
allowed to be the bravest of all the brave,
John Cutts. Conspicuous among the Dutch
troops were Portland's and Ginkell's horse, and
Solme's Blue Regiment, consisting of two thou-
sand of the finest infantry in Europe. Germany
had sent to the field some warriors sprung
from her noblest houses. Prince George of
Hesse Darmstadt, a gallant youth who was
serving his apprenticeship in the military art,
rode near the king. A strong brigade of
Danish mercenaries was commanded by Duke
Charles Frederick of Wirtemberg, a near kins-
man of the head of his illustrious family. It
was reported that, of all the soldiers of William,
these were most dreaded by the Irish, for cen-
turies of Saxon domination had not effaced the
recollection of the violence and cruelty of the
Scandinavian sea-kings ; and an ancient prophecy
that the Danes would one day destroy the
children of the soil was still repeated with
superstitious horror. Among the foreign auxi-
liaries were a Brandenburg regiment and a Fin-
land regiment. But in that great array, so
variously composed, were two bodies of men
animated by a spirit peculiarly fierce and im-
placable, the Huguenots of France thirsting for
the blood of the French, and the Euglishry of
Ireland impatient to trample down the Irish.
The ranks of the refugees had been effectually
purged of spies and traitors, and were made
up of men such as had contended in the pre-
ceding century against the power of the house
of Yalois and the genius of the house of Lor-
raine. All the boldest spirits of the uncon-
querable colony had repaired to William's camp.
Mitchelburne was there with the stubborn de-
fenders of Londonderry, and Wolsely with the
warriors who had raised the shout of " Ad-
vance " on the day of Newton Butler. Sir
Albert Conyngham, the ancestor of the noble
family whose seat overlooks the Boyne, had
brought from the neighborhood of Lough Erne
a gallant regiment of dragoons, which still
glories in the name of Enniskillen, and which
has proved on the shores of the Euxine that it
has not degenerated since the day of the
Boyne. "

A great dramatic, if perhaps slightly opinionated, description of the opposing forces at the Boyne, from "Battle of the Boyne," no author given. Interesting to see the myth of a Finnish regiment repeated, and the description of the 5th Regiment as Colonel Cutt's, whereas I'm pretty sure it was Edward Lloyd's