Adding variation to design in printful but show as same product

I need to add variation to the product. I have a light color design and also a dark color version of the same design. light color will not work with white shirts and black color will not work with black shirt. I wanted to add variation so that light color and dark color design show up as the same product but as variation.. Manually syncing would be bad idea for 7 color shirts of 7 sizes ( 49 variations ) because I have to add image for each variation and sit for hours doing that. 
Let me know if there is an better way to do it or not. These options are available in shopify and wix and woocomerce to modify the print file for specific design and also add new design as variation to same product.