You can paint over them or tile over them.
You can buy paint specially made for tiles or appliques that can be put right on top of the tiles for decoration.
Daich wall, tile or countertop kits can make a great transformation to old ugly tile.
I just pained my bathroom tiles, so this is an option! Here's the tutorial for you: https://www.youtube.com/watch?v=Zhct4NvU_lI