“I believe the Infantry was white.”
Light blue. Trust me on that one. I wrote a book on the Civil War USCT which featured colored plates of soldiers in all three branches. Boy did I have to document everything. (It was for Osprey, Ltd.)
During Civil War and well into the Indian Wars, even rank insignia was colored to match the service branch. Cavalry had red stripes and rockers, infantry light blue, and artillery red.
Actually, you're both right. The color of infantry facings and trouser stripes was either white or light blue, depending on the time frame. During one period, the facings on the uniform jacket, and color of the rank chevrons was light blue, while the trouser stripes were white. Since the trousers were already light blue, white provided a better look.