This is sorta of what I was thinking too, if it wasn't some gene exclusion concept. The patterns just aren't nearly so grand on a pale horse!
You mention greys- I am correct in assuming you would stay away from that as well, since it would negate the patterns once the horse went grey, right?
I understood you meant that the genes would not work that way by the term "gene exclusion" which is not at all accurate. However, I think you would be right (in general) saying there IS an intentional "exclusion" (though I'd be more inclined to say it's more of something to avoid than something as concrete as being excluded) BY THE BREEDERS (not the genes!!). Yes, same with grey. If you are breeding for color you want to get rid of anything that will hide/diminish that color, it's all about how the horse looks (though on a larger scale as we are talking about here obviously conformation and suitability are important, no good breeder breeds solely
I agree with you on palomino and buckskin, keep in mind though that the genes that give the Appaloosa's their pattern tend to do weird things to the base color (for example, a lot of black turns into a dark red so you can have a horse you'd swear was a chestnut and is actually bay.)
I don't think the buckskin's points are paled out (though see the above comment) are you seeing the "frosting"/white on the mane and tail? Normal for buckskins, spots or no, (google buckskin frosting) but if the horse has white where the hair is growing out of the hair will be white. I don't think the spots are "pally" and as far as them being darker I don't know the exact nuances of the color patterns but some horses, no matter what the base color, have darker as well as white spots. (maybe one of the experts can help us on this!)
Of course there are things that dictate the color/the name! Not sure on the reverse thing, but my understanding is-
To have Appaloosa colors a horse has to have the leopard gene.
With this gene the horse will have Appaloosa traits, including varnish roan (some varnish more than others).
See how the color stays on the bony parts?
This gene will ALLOW the horse to have color- one copy with a pattern the horse has spots
Two copies with a pattern the horse does not have spots.
Then there are other genes that control where the pattern is (blanket or leopard? snowcap or fewspot?) some of which have been pinpointed, and a million more that control the exact spots, size, pattern, etc. So you can even have a horse with the genes for the pattern that doesn't have a leopard gene that allows them to express! When bred to say that varnish roan up above you could suddenly have a baby covered in spots!
Appaloosas tend to roan out as they age too (see the varnish roan above, it's part of the color!) so the same horse may look entirely different in a couple years.
Check this out Drafts with Dots: The LP gene
Does anyone know where that cool little graphic is? A rearing horse and you plug in the genes and see the colors change? I need to find that!
Hope that made sense.