Multicolor cards are easier to discard because they match two or more different colors. They are mainly used in expansions, but four color cards would easily be added to the main sets of Crazier Eights as well.
I have been developing the multicolor card frames, and there are two options regarding how they will look. The first option is based on the regular card frame, and the second option is based on the current wild card frame. Take a look below:
You can let me know what you prefer in the poll below.