Scratch

To change the variable color, (and this may not be right, for I've never done it) you have to shift-click in the "R" in the Scratch logo at the top-left corner of Scratch. It may be a different letter than "R". Also, I would prefer not to try random letters, because they may do other things that can mess something up. 
     In case you didn't know, you hold down the "shift" key and left-click, which is why it's called shift-click.

Shift click the R in the SCRATCH logo in the Scratch application. Then choose turn fill screen off.

Now right click the variable you want to change the colour of until the little icons come right around it. Now choose the menu for me icon. Click change color. Choose a new colour. You're done!