Great idea and the art is really nice.
Outside of 'same number + colour' I honestly found it hard to work out the rules cause I didn't know what the rules could possibly be. A reference of all rules would be useful if this is worked on more.
I think it'd be really useful to see the last 4 played cards to help work out the rule too. Some cards are played so fast that you only have the most recent card to help.
Being able to change colours/numbers when its not your turn shouldn't break anything.
The cards continued to be played after the game ended which may cause a null ref at some point.