Textures for cloth-randimized NPCs

Question

I have this thought of making this "dick out" mod for all the male characters in the game and all muscular pokemons. I have encountered a problem with the textures when dealing with the "muscle guy NPC" model because it seems there are multiple color schemes for NPCs like this. I replaced the texture for the Muscle guy with the file attached.  However, the color of the dick is always colored as the color similiar to the pants. I don't know how I can solve this or is there another way to achieve this.