I cannot claim to be an expert on roman military uniform colours (I did study classical archaeology almost to BA level, but my expertise was more on greek temple architecture and the antonine wall), but I would suggest that safe choices are a deep red for legionary uniforms, and white (linen?) for auxilia.
Shields are a completely different issue - unless recent (last 10 years) research has shown otherwise, this is guesswork - few shields still having original colour survive to our days.
In all, I think the link archangel1 suggested is worth checking out, they must have done their research. At least the section on legionary equipment on their site looked good - didn't have time to check out the rest of it.
Marko