pick a colour. this page exports it for real, in your browser, through the same encoders you ship with, then counts how many pixels come back exactly the same value.
solid = a full 128×128 fill of your hex. patch = a 96×96 square of it on a #808080 field, counting only pixels 6px inside the edge (the flat interior). exact % is the share of tested pixels that came back byte-identical after one save. nearest = the most common colour the survivors turned into, with the biggest single-channel shift. a flat fill of one colour either keeps the value exactly or moves it uniformly; edges are where it bleeds.