Changing font color/highlighting font in drop downs

I am wondering how to change the color of the font of a drop down or highlighting the answer depending on what option is chosen.

For example, I have five options in my drop down: A, B, C, D, N/A. When "C" is chosen, I need the form to show it as yellow. When "D" is chosen, I need the form to show it as red.

Does anyone know how I can accomplish this?

I also don't mind if it highlights the chosen answer or just changes the font. I just need some way to color code the answers.

Thank you in advance for any help!