I own a few perlinos. I'm doubtful they could consistently sweep (or ever sweep) a color class
(but oh... their foals will!). However, halter is how the horse is put together, vs. how attractive the judge personally finds the color, and you shouldn't be discouraged about showing a perlino in halter. Some have done really well.
To me, color class is fun to do if you have a nicely colored horse, but the only classes that are meaningful to me when it comes to wins (and this is just ME and my opinion) are halter and driving. But some love color and some love liberty... halter obstacle, hunter... it's so cool with minis that there are so many ways to show them and so many opportunities to be competitive.
Color class, especially in AMHR where conformation is not a factor, is just about what color the judge likes the best that day. It's like you may really like the color
red, but to me, purple is much prettier