Interesting images. It appears from the parent site, mostly in Russian, that these may date from the C19th. viz:
"19XX. Bucks militia 1793 – 13 Plates"
If so, presumably the paintings were taken from earlier originals
The uniforms show a transition between the 1780s and 1790s, coats still with 1768'cape' collar, knee-length [woolen] gaiters, and hats now minus lace binding and with a profusion of regimental feathers – red & white tricolour for the serjeant major, red for grenadiers and drummers; red over white for the rest of the battalion, but yellow for the exotic section of the band.
STOP PRESS. The images are from a set of paintings apparently made by Sir William Young in 1793 , of the 'Royal Bucks King's Own Militia'- a title granted the regiment for guarding King George III while he was bathing at Weymouth in 1794 A long way from Buckinghamshire; presumably they were on anti-invasion duty.
See the website of the Buckinghamshire Military Museum Trust
(BMMT): bmmt.co.uk/our-collections
