Those are the US rules, in Canada there are no restrictions on colour. (At least not since the last time I checked)
A woman here showed in a red saddle pad for Red Fridays to honour her son in Afghanistan.
There was a lady that showed GP in a very dark navy tail coat and a bright navy saddle pad on a bay horse and it looked absolutely repulsive.
On white horses, sometimes black pads are better so you aren't showing off the minor stains, and I have shown other coloured horses in black pads too during inclement weather. You aren't going to get a comment on your test (unless you're getting judged by Cara Whitham) and ou aren't going to get funny looks. Black is just as kosher as white pads.
Thanks. I'm kinda nervous. It's been about 6 years since I've shown at all, and the first time ever I'm specifically going to a dressage show. So I'm starting out at the very bottom. Cause that's the best place to start over right?