The issue you're having is that you're bringing the tile samples into the old all-white space - and since they stick out like a sore thumb, they seem "dark"

Trust your instinct - get the darker tile you like. Just use the samples to coordinate with cabinetry, hardware, paint, etc - and make sure there's sufficient lighting in your plan.

Thank you for the advice & perspective adjustment - it helps!

Thank you for asking the question! I want the bathroom to be about water: when in the shower you are in a drop of water and in the tub, you are near a water source.
I saw marvelous glass mosaics in green/blues/aquas/ but they look too dark in the house. So I was wondering what to do..., until this post. Thanks again

No problem, Holly. Did you make your selections yet?

Yes, i have chosen a green/blue glass tile mosaic 'malachite blend' for wow and a light turquoise glass tile for the field. Bright white grout.