Check boxes change to square when edited

I've created a form with circular check boxes... so check circles I guess. The default color for the checks is obviously black, I want to change their color. When I go into the Properties > Appearance menu and change the color, the check box turns to a square. I cannot change it back to a circle unless I undo the change, which also changes the color of the check back to black. Am I doing something wrong? Am I not doing something that would prevent the circles from turning into squares? Is this normal? Thanks!