Hi Johan.
The colour party is a seperate entity, not attached to any company. It's associated with the battalion company because traditionally it stands in the middle, so the colour party is behind that. The flank company is on the left (the clever fast soldiers), used for skirmishing actions, and the grenadier company on the right (the "less clever", but brutal soldiers), used for insane actions.
Hardly any soldiers in the regiment were from Gloucestershire (hence the lack of intelligence and good looks ) at Waterloo. The 28th was originally raised in Portsmouth (hence Devon) and wasn't associated with Gloucestershire until just before the Peninsular War (when the recruiting party's were sent out). Why it was associated with North Glos I don't know, and why the 61st was associated with South Glos I don't know. Conversely the regiment associated with Gloucestershire at this time was in fact the 24th foot.
I wouldn't read too much into regimental associations, they were chosen with a pin, and don't forget that of all the British Army that fought at Waterloo, only about 28% were from The British Isles anyway.
Right that's enough history lessons for now
Richard