Colours were unit standards used especially in the period when communications was a bloke with a very loud voice (a bit like now when comms go out and there's no Vodaphone coverage).
The 'Trooping of the Colour' was a process by which the squaddies were shown their flag so they could recognize it on the battlefield - and hopefully rally to it when things went tits up.
The loss of a unit's colours in battle was the greatest shame a unit could suffer (similar to the artillery losing its guns) - matched only by the glory if you managed to take another unit's (i.e. Napoleonic Eagle standards). Three drunk Toms liberating a friendly unit's colours in a daring midnight raid, after an evening in a Sticky Carpet is NOT the same ... no matter how daring! ... Robbing the Stars 'n' Stripes from the Las Vegas Hilton - five storeys up - however, is!