Quote - Thanks for the advice everyone, much appreciate it. I will also look for the Normals_Forward setting, I assume it's where the nodes are in the Materials room.

**It is a check near the bottom of surface node.  On this pair of shorts, if unchecked, the inside will appear black, with set, the fabric color shows.
**> Quote -

... and the whole render had a sort of grey tone to it, which never happened before, and I haven't changed any lighting or render settings, so I guess I've got my work cut out for me.

That sounds like Gamma correction is on (which is good), but you will have to adjust lighting and maybe some of the shaders.