After years of buying clear or white bath mats, even though I find them completely impractical, I finally found a BLACK bath mat for my tub/shower.  An important plus is that it is extra long; previous bath mats I've had were much too short:  I was protected while under the shower, but if I moved to the side to shampoo my hair, I was relegated to the slippery part of the tub.  Thanks to this mat, this is no longer a problem;  it covers the entire bottom of my tub.