Coomassie Blue G - 250 is a useful stain for protein detection in PAGE gels. Coomassie staining gives blue bands on a clear background, with a sensitivity of 100 - 500 ng/band. The G - 250 dye is converted to a leuco form below pH 2-3. The leuco form regains color on protein binding, and is the basis for the Bradford Protein Assay.