i usually do washes of brown over 2 close "but not close enough" parts like forearm to bicep. though i also prefer dirtied up looking customs.
a list of factory skin tone matches may be near impossible. for lots of reasons the plastic color might change from run to run at a single manufacturer at any time. also i think i've seen some brand new heads from like BFS or similar that were painted flesh over solid colors, like a blank green head. so that might be a much harder thing for the factory to use the exact same paint color run after run.
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The more you run over a dead cat,
the flatter it gets.
-Anonymous