Bryce seems to do odd things reading a mtl file. It sets the diffusion channel to the texture, and a strength of maybe 80; ambience is black with a strength of 100 and specularity is 100 whether you want an oily look or not. I've never found a way of fixing this automatically, so I have to adjust it by hand. Set diffusion and ambience to the texture and juggle around to get sensible settings depending on your image.