Product image changes thumbnail when sold out?

I have a client who wants to have a sortof modified donation thermometer on their site. In essence, they want to show a grid of boxes where each box is assigned a dollar value. When all of the boxes are sold, they've reached the amount needed to sponsor a student for their program. Ideally, they want sold out boxes to appear a different color to very obviously indicate what is sold and what is still available. 
I was thinking I could do this with Commerce and set each "box" up as a product with quantity 1. But I'm getting stuck on how to have the image or color change when the quantity drops to zero. Any advice would be super helpful!