(c) prefix indicates materials applied to either parts or assemblies within assemblies at a higher level, these overide materials applied at lower levels. the hierachy of faces, features, parts then assemblies still applies first
but with (c) prefix being dominant where all else is equal.
Does this amke sense to you?
Also use of solidworks materials appears to effect the final appearance using the same hierachy rules, at least most of the time. I am still investigating.