From the pattern description: The above mittens are just an example of what can be done with these blank charts. Get a pencil and fill in the squares as you see fit, then get knitting! Print the chart out at least twice so you can design different backs and palms. If you go over 7 or so stitches in one color, weave in the yarn you’re carrying, or else your fingers will snag the loops when you’re putting them on.

This site has more charts than you can shake a stick at.