I would not bother with tile for the base, but select a cast base from Kohler in a color that matches the tile. No leaks with this and easy to install. All different sizes and shapes.

https://www.us.kohler.com/us/browse/bathroom-showering-shower-bases/_/N-2d8r

What a phenomenal idea. The shower is already installed so do they custom make these pans?

As one who thinks the shower pan should be installed first and followed by shower walls? I don't like the entire concept and just be prepared for leaks. Maybe it's time to do a bath in the tones you favor, and not peck at lipstick solutions.There are plenty of dark /light/warm/cool porcelain tiles. Show the entire bath in a photo.

Why are you doing this? Is it currently leaking?

I agree with Jan no matter what pan you choose it should have been in first now just looking for trouble. I too am wondering why the issue at all and BTW neither of those choices would work with that tile IMO.