I don't know what you pixel with, Doppleganger, but when I first pulled your tiles into Photoshop to play around with the contrast for my own edification, I noticed that they looked a lot better, contrast-wise, in Photoshop's CMYK proof setup, which is the default. Switching to to Monitor RGB allowed me to see what it will look like when it's saved and viewed outside of PS, and revealed the low contrast.
I don't know if this has any bearing at all, I just thought I'd mention it.