In a certain code, 526 means sky is blue, 24 means blue colour, and 436 means colour is fun. Which digit means fun?

The digit for fun is 3.

526 = sky is blue and 24 = blue colour share 2, so 2 = blue.

24 = blue colour with 2 = blue gives 4 = colour.

526 = sky is blue and 436 = colour is fun share 6, so 6 = is.

In 436 = colour is fun, 4 = colour and 6 = is leave 3 = fun.