How can I change the background color in a record grid cell?

I have a record grid widget displaying PreACT scores and semester two grades. I would like to color-code the grades in each cell, A as dark green, B as light green, etc. I am able to use a recode for the field to change the font color (ie "A"), but would prefer to change the background. I have tried " A" but that is not working for me. Suggestions?