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Actually just using brake cleaner and MAYBE a toothbrush should do the trick. A full can should do the trick.

I have 2 other possible strategies that I wanted to run by the experts before officialy recommending them ;)

A)
1) Soak in alcohol
2) Scrub with a toothbrush
3) Another soak
4) Another scrub...

The color is just an indicator. Unless you're familiar with the particular stone, you should examine the stone surface under a magnifying tool.