Gents,

Just a couple of quick questions as I paint pre-1700 Cuirassier Du Roi.
Would the officer and guidion officer be in the regimental uniform or in clothing of their own choosing? And what colour are the riding boots buff or black?

Black boots. They would almost certainly be in a better quality of the common men's uniform but there were always some exceptions!

Black boots indeed from the 1660's.

As for officers they would have worn regimentals from a relatively early date, certainly by the 1690's and the Nine Years War and quite conceivably as early as the Dutch War. As their name implies, the Cuirassiers Du Roi were a royal regiment and as such were more likely to conform to the November 1671 royal order than the régiments de gentilshommes.

And as J1mwallace says, officers' uniforms would be made of finer cloth with silver or gold lace and buttons.