Huh? What Blob you talking about? Not THE Blob. Sure, there have been plenty of b&w movies about blobs - The Creeping Unknown, The Quatermass Experiment, Kaltiki the Immortal Monster, et al. But The Blob, star of The Blob, made his classic debut in glorious De Luxe color. I remember that he started out bright blue, and got redder and redder the more people he dissolved.
My bad (on two counts). I'm pretty darn sure this isnae called The Blob, but when I saw the movie it was at the base theater in 1960s Germany, and somehow black 'n white (or maybe on my old TV?) The changing color aspect sounds cool, and I may have to watch again (and Return of...)