post factory color case hardening is a process where creating case colors is a goal...if a high heat process is utilized, those colors can be a by product of the rehardening process...sometimes a cracked frame can also be a by product of a reheat treating process...and then there are the efforts to straighten warped re heat treated frames, which may also result in cracked frames...also, if a reharden frame is not correctly tempered, it could be as brittle as glass, and may crack under the stress of shooting, especially with mag loads...
