The Transparency Trick was a bug that could have been done from 2007 until 2009. There are some body colors on ROBLOX's body color change that make you white. When the old studs were still on ROBLOX this Trick/Glitch was possible. It was only available to the ROBLOXians who had the old, solid body (Used from 2006 - 2009). When the old studs where being used, the method for applying the body texture, and caused a Transparency Glitch, making your character invisible. If you made your body invisible and then put a certain T-Shirt or Shirt or Pants on, you would look like a certain object. But since the body updates, the glitch is no longer possible. People often exploit the body to look like the old studs, thus activating the glitch. It is sometimes found on abandoned ROBLOXians.
Currently, players glitching and whatnot are being persecuted. Even for a meager transparency trick, the result may be a ban or worse.
There are a lot of scams surrounding this bug. As the player will said to buy the specific shirt or pants (which usually is theirs) and said it will make their avatar "invisible". However this is proven false and it isn't possible to be invisible.