Starbound uses a hex color system to assign colors to races to provide the various ingame options for players and npcs. From a list provided, they can be expanded or even removed if one feels like it. The slime race uses hex colors that assigns them colors that are also partially transparent.
Since this mod uses that same system and applies it to the fat body armors, it can match up with whatever player or npc that gains weight. One restriction of this armor though is the inability to hide the original body, rather it has to completely cover it and account for its animations. As the only invisible option in the game is all or nothing, it cannot target specific body parts. Thus if a race that is transparent had any support. You would be able to see the original body underneath the fat body. It is especially bad for the blob size with the increased height and trickery with the arms.