White ebonies and mosaics aren't able to be differentiated by phenotype only. You need to know what their background is to be completely sure. Because he/she has ebony in the background, I would call him/her a white ebony. You'd know for sure if you put it into breeding and an ebony popped out, that it was a white ebony. Or, if after I think its 50+ kits, an ebony still hasn't appeared, you can almost be certain it is a mosaic.