From the Uniformology booklet The Army of Spain in the American Revolution and the New World by J. Sloan Cranz, which I own.
Illustration of a 2nd Regiment of Cataluna Volunteers drummer shows no turnback, just a straight coat, but the cuffs and facings are yellow with white "teeth" on red trim on the cuffs and the collar.
Illustration of an officer Volunteer Regiment Cataluna shows a straight coat lines red with plain red cuffs and a red vest with blue britches.
Illustration of a grenadier of the Regiments Soria 8, Navarra 25, and Aragon 28 shows red turnbacks with red cuffs and red britches.
Illustration of a grenadier of the Flandes 28 Infantry Regiment shows medium blue turnbacks, vest, cuffs, and collar.
Illustration of a musketeer of 10th Regiment Guadalajara shows red turnbacks, cuffs, and collar with a red vest.
This booklet has more uniform illustrations. It is available from uniformology.com .
Jim