How to make change the colour of a character when he go in a special zone?

Hi,

I need in my prototype of game to make change the colour of the character when he go in a special zone. I just don’t know how to program this :confused:
The special zone is represented by a button of a colour. When the character will walk on this button, his colour is supposed to change to the colour of the button.

I’m very sorrry for my English.
Thanks for the help