Ted Spring in his book Sketch Book 56 Vol. IV. Gives the 1769-1771 uniform of a drummer as this: Blue coat with red collars, cuffs and lining, with blue trousers. The two rows of lace is “Bourbon Livery”. Spanish infantry did wear white coats and perhaps some one was confused. I am not sure if the uniform changed before the time you are interested in.
To Join the Company of Military Historians click here