Rainbow as a wildcard!

[FerLuisxd]

Is your feature request related to a problem? Please describe.
Currently, there is no way to way to create a room where the rainbow is considered a wildcard (not as a new color)

Describe the solution you'd like
For example, you got a rainbow 3 on my hand and a blue 2 on board. I'd like to be able to play the rainbow 3 and be on top of the blue 2.