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.