While this in and of itself isn't 100% true, the game works on Game Boy Color and Game Boy Advance. And when I played it on the Game Boy Advance, it was indeed in color.
No, this is a romhack that aims to make a DX version of Super Mario Land 2, in a similar fashion to how Link's Awakening DX gets a colour version of the original. One feature that some people would take fancy on with this hack besides the added colour is that the player can swap the playable character to Luigi.