Lin, The only way I know to get a deep color change on rawhide is to dye it wet before putting it on. I've used rit dye in fairly hot water to get good color changes on braiding string hides. It will get deep enough to stay.
Sealing it is pretty tough, rawhide never quits pulling and shrinking. Most coating type finishes crack. On braiding I've always just used a rubbed in coat of Feibings white saddle soap. I'm trying some stuff made for rawhide, so far I can't tell the difference from the saddle soap.
I've made some camera and bino cases out of rawhide (light and very tough) I've just used amber shellac on them. It gives them a nice amber tinge and when it lightens up from wear I just give it another coat. It's also what I coat my rawhide saddle tree's with.
Hope this helps. Robin