does sand blasting remove the HAZ rainbow?

Yes it will remove any oxides.

Make sure they glass-bead blast the frame. No garnet or flint shot. They are way too agressive for thin wall tube.

There are also some new plastic shot medias that work well without removing metal.

Baking soda or walnut shells (animal bedding for hamsters and little rodents at pet stores), works well and is less aggressive than glass too (maybe less than plastic media). Stay away from aluminum oxide, I'm mentioning that because alot of supply stores stock it. Do a google search in the groups for abrasive blasting media, it's amazing the stuff people use that works. good luck, walt