In order to replicate secondcolour you will need to create duplicates of all of the sprites and erase everything except the part that you want to change colour. Then recolour it green, obviously. After that create a lua to put those sprites on top of the player sprites and handle colour changing.
I remember the post for secondcolor mentioning clipping issues.
Also i also remember that when i went invisible on Spectrum with a flag, the secondcolor didn't disappear.
I think that's proof that it uses another sprite.