Well....seen as I'm an artist...lol!....I'm going to give my opinion in terms of color opposites.....These colors are opposites, so they POP against each other:
(this is how I like to match things up nice)
Yellow tones (palomino, perlino, cremellos) = purples, the lighter the horse - the lighter the shade of purple
Red tones (rich chestnuts/sorrels and blood type bays) = greens, again the lighter the horse the lighter the shade
Orange tones (light chestnuts/washed out bays) = blues, again the lighter the horse the lighter the shade
Black horses = these guys can wear anything! (bar white, not a fan of white though!)
'White' horses: anything neutral or washed through with white, ie. light colors
(I used the term 'white' horses in terms of visual, not genes
Roaned horses: again go with the base coat color and dilute the color of tack to match nice, ie. red roan who is greying out I'd used a neutral saddle pad with green tones in it.
Essentially, I like to match the intensity of a horses color with the intensity of the color of the tack. Ie, strong color horse = strong color tack in a color opposite
Did that make sense???
As for the 'fluorescent' colors....they don't count! No such thing as a fluorescent horse!