Viskovatov states that Russian foot gunners were ordered to wear the same trousers as the line infantry musketeers and grenadiers in December 1807 - i.e booted trousers for winter and overalls for summer.
Grey cloth trousers were ordered in September 1808 but do not seem to have lasted for very long. In 1809, green breeches were ordered for winter wear :
"8 October 1809– Lower ranks of Battery, Light, and Pontoon companies were ordered to have dark-green winter pants, the same color as the coat, and mounted gun handlers and train noncommissioned officers were additionally to have black leather along the inner seam. After this, gray riding trousers were no longer authorized for them (Illus 1634)"
So white breeches for summer dress and dark green ones for the winter uniform it is, though things were never simple in the Russian army and the booted white winter breeches authorized in 1807 may well have continued to see service alongside the new green ones (though probably not in the same battery).
Here's a link to an English translation of Viskovatov's text in case you need it :
http://marksrussianmilitaryhistory.info/V12.htm#9