I don't know what the CSP command for this may be, but it looks like you want to find and play with any options related to image color depth or color palette. In Photoshop when saving GIFs there'll be multiple options for generating color palette (since GIFs have a limited color depth) and which option is selected will effect the outcome. I think there may also be options for manually adjusting color selection, which might be what you want to do.