Morning Viriato!
Apparently, the story with trouser colours (if I can recall this correctly) is this: British troops of the period usually wore looser white cotton trousers for summer wear, and service in hot climes, so these would be fairly standard for the Peninsula for example. Grey trousers were usually reserved for winter wear, but for one reason or another seem to have been the type worn by the majority of British infantry units participating in the Waterloo campaign (which seems appropriate enough in hindsight, as even though the fighting took place in early summer, the extremes of weather seen there - torrential rain, mud, etc., would probably have made them a good choice).
However, the Guards units, who were eternally a law unto themselves, seem to have worn white trousers in a significant way during the Hundred Days - at least according to most reference pictures and descriptions that I've come across. But that doesn't mean that grey trousers weren't worn by some Guards units.
So the short and sweet answer is essentially that both Britains and King & Country's individual takes on 1815 Coldstreamers are historically accurate. Though depicting the same regiment, they do feature different sub-units, as K&C's recent Coldstream releases feature members of one of the regiment's centre companies, whereas the Britains sets portrays members of the regiment's light company involved in the defence of Hougoumont. It is certainly conceivable that due to supply problems or a slow pace of the same, that two different companies even in the same battalion could be wearing different coloured trousers. After all, these weren’t considered quite as essential a uniform item, and an aid to recognition, as the red tunic for example.
It is quite perplexing stuff though, and exceptions to the norm like this do seem to pop up an awful lot with Guards units, as their traditions and practices past and present often seem to vary from the rest of the British Army. For example, since the first time I ever read a serious historical work on the Napoleonic period (I think it was an Osprey title many moons ago!), I’ve been aware that the facing colour of each individual British infantry regiment, as displayed on the collars and cuffs of the tunic, was the same colour that was used on the regimental ensign. When we come to Foot Guards regiments of the period though, as correctly displayed on K&C’s figures, we have dark blue uniform facings…..with a crimson/maroon standard???
Very confusing, to say the least!
Anyway, hope this is of some help to you mate!
Cheers,
Molloy.