Did you know that the classic SMB had a map screen? Well it does in the Gameboy Colour version. If you want a map that acts like the one from NSMB, having levels turn red when completed, then this one is for you. Read the Readme for tips on how to use.
A minor warning, since this is technically from an 8-bit handheld, be aware that clashing is possible. Personally, however, I don't think it's that bad with Mario's overworld sprite... if you compare it to other 8-bit graphics.