Fun fact: I live down the street from Edison. But it’s cute that you’re assuming. ;)
I think, personally, that darker saddles look better with lighter colored accessories. The saddle I have for my bay giraffe is supposedly chestnut colored (that’s what the ad claimed it was) but It looks lighter to me. But it’s still a good color on her paired with a patterned saddle pad.
I personally love darker saddles, and I think the lime green would look better with the darker colored saddle. And it would look good on your horse too. If you want to find a good deal and get an entire tack set like I did (cause I HAVE to have everything matching) there’s usually great deals on E-bay.
To answer the QHB (quarter horse bars) question: this refers to the placement and general angle of the bars themselves, but actually has little to nothing to do with the breed(s) that it suits. To make things even MORE confusing, there are full QHB (for wider backs), semi-QHB (for slightly narrower backs) and then different gullet withs for each, and every saddle maker is different. I won’t go into Arab bars since I don’t know what “fit” they are geared toward really, but haired saddles make a noted effort at allowing shoulder space for gaiting which makes sense, however general fit is more important than the name of the type of bars. Western saddles are extra tricky as well because they can’t be flocked like many English saddles can so they are less customizable for the horse.
Google pointers for how to tell saddle fit and maybe join some forums with knowledgeable people (horseforum.com is a good resource!), but don’t get hung up on saddles being “breed specific.” Good luck in your saddle search, Anon, and good on you for asking questions! :)