When the introduction of skin packs floods the workshop with variety of skins, builders loves to combine multiple skins to create more colorful and visually appealing machine. Same goes to me, but while testing multiple skins to check which one goes well with others, I sometimes lose tracks on how many skins I've tried and there's usually some leftovers skins that should not be in the final version as people will be confused why they need to search that skin.
This would be useful to keep track on how many skins we have used, and should be located when you hover to the block amount at the machine stats info. It should be sorted from the most blocks till the least block, and the height will adjust according to the amount of skin pack the machine used.
Download here if you're interested in that plane.