A few warnings, don't use text (it creates a layer that somehow corrupts it in the game), and I believe the only programs you can use to make it are Photoshop or GIMP (GIMP is free, google it). And as Brittany said, make sure you keep the colors a gentle mix if you want to be able to climb them. The more contrast, the steeper the height. Also, blur tool is your friend, it helps it mix nicely.