Chris,
Good eye and you are entirely correct. The 1956 uniforms (home and roads) jerseys and pants were made of a nylon/cotton durene fabric. The road grey fabric was not particularly color fast and those tended to fade, to the point of looking just off white. However, the uniforms collar and placket are lined with flannel material (white for the homes, grey for the roads) and this is very easy to see when they are compared side by side.
The attached photo comes from the rear cover of the 1956 Cincinnati Redlegs Yearbook (Revised Edition)
Dave Grob
DaveGrob1@aol.com