Making a fillable PDF need some selections to be a different color

I'm in a bit of a pickle. I am trying to make a grade sheet for work, and not sure exactly what to do. I think the best route will be to use a dropdown list so a user can select certain symbols for grading criteria, but I need those symbols to be different colors depending on what is selected for example: + needs to be green, - needs to be red, and U needs to be yellow.

I don't know how to make it different colors, or if its even possible. Would appreciate any input you folks might have on how to do it, or even the best route to take.

Thanks!