It would surprise me to see any secured source for that theory. As far as I have read, I never stumbled accross such comments whatsoever. If it was sort of a preference, perhaps to pronounce inner military social standards whatsoever, this may have been the case but then you will certainly not find a 100% valid evidence in any book.
On the other hand, in mid-1813, the bulk of the guards still wasn't more then a shadow of the past. Most of them regiments had suffered badly in the Russian campaign, a number of battalions had no officers at all and some just existed in theory - on the roll. When the empire went over the brink in 1814, the 'guards' were in no good shape and far away from the glory of the years before 1812.
Taken this into account, and taking into account the hasty rush of raising troops and reorganizing everything in 1815, I have my doubts that the officers of guard regiments had no other things to do then care about horse colours when it was quite a challenge to get enough horses for all the regiments at all.