In Tricky: 6th color (10cards) you play with an extra set of card of another colour ie rainbow colour.
In Very Difficult: Multicolor (10cards) you also play with an extra set of card. However, this set of card will take on any colour clue. For example: if the hand is m3 b4 g2 r2 and you clue it red, it will be r x x r. If you then clue it again with blue, it will turn into m b x r.
Hope that answers your question.