Royal Blue is a really good color on chestnuts or red!
A have a chestnut who surprisingly looks very sharp in red!
Navy is always a good option too :)
I have a neon green/yellow pad for my chestnut. Looks great!!
Navy or black really looks cool on chestnuts
Um blue purple black white
Lime green, purple or any type of blue.
Purple and teal blue look good as well.