My last finish has a dark purple mottled back and a lot of cream blocks on the front. No show through with Hobbs 80/20. I never worry about show through even with a poly batt as long as the white is a decent weave. I used a purple varigated thread on the back and cream and tan on the front on the last one.
Marshall's Dry Goods has some wide backings in mottled colors. Orange?? I don't remember.