I had someone mention periwinkle to me...it may be invasive though. I cannot use it because my area is all sun.

Just a suggestion, I grow Corsican Mint It spreads, but is not invasive. It has tight compact bright green leaves, and almost looks matted, sometimes getts tiny yellow flowers. It does take light foot traffic, but heres the cool thing every time you step on it, or even press it with your finger it releases a nice spearmint scent! Yummy. It may not be what your looking for, just thought I would share, I really enjoy it, a lot of people use it like moss to fill in cracks of stepping stones. It smells heavenly!

I had a lot of trouble keeping Corsican mint alive since it likes moisture but it self-seeded into my path with lava rock and seems to like the moist micro-climate under the rocks, so putting some small rocks down with it might keep it alive better.

You might enjoy looking at photos in the Stepables website for inspiration.

Here is a link that might be useful: Stepables