What Aaron said.
There was no difference between full and campaign dress at the time : the coat's colour remained the same regardless of the circumstances. Since clothing was issued on a yearly basis, what many regiments did was use the previous year's coat for campaign wear, thus saving the new coat for parades and ceremonial occasions and making the garment last two years instead of one. In that case, the old coat's tails were generally cropped to provide material for mending and repairs, and the expensive button lace was removed and transferred to the new coat.
At least this is how the system was supposed to work. If a unit failed to receive its new clothing issue, which happened on quite a few occasions during the war, then the men would soldier on with the previous year's increasingly tatty coats.