Excel tabs are grey/silver - no color

Hi - I just opened an excel workbook that I was making edits to yesterday that I had color coded tabs in but now they're all grey/silver. I tried searching for a solution on google, but all the articles were related to buttons being "greyed out" or not enabled. That's not the case here. My tabs are supposed to have color but they are the color grey. Does anyone know what is going on?