I am inclined to look at what a registry has called a horse, and then assume it is a different colour lol. That is how much I respect their colour knowledge lol.
Po and ND will have seen me say it before, but I will say it again. Here in Australia, buckskins and duns share a registry. They go in the same classes at most shows. Most people use the terms to apply to both colours, and quite happily interchange them. All it is is a lack of education about the colour genetics - just like a registry body who would accept buckskin and palomino, but not cremello or perlino.
And by the way, a perlino would test as bay.