if it's the exposed area only (and not the entire sheet of paper), and you are in fact seeing an image before it turns black, it sounds like over exposure. a lot of factors there: f-stop on the enlarger lens, negative density, exposure time, filter calibration on the color enlarger, etc. With more details about what is going on I'm sure you'll get some sound advice here in the forum !
Doing test strips always help out if you're relatively new to working in a wet darkroom.