Hey,
As you haven't mentioned what have you coded,
i am telling you the general steps of doing that.
Firstly, You should know about button's setBackground() property where you can pass color code as an argument for setting background-color of button. ex- "setBackground(Color.green)"
You can learn about it
Here[
^]
Secondly, You have to handle the mouse-enter and mouse-exit events(associated with button) and change the background property of button accordingly(change on enter and restore on exit).
You can learn how to set and handle those events
Here[
^]
Happy Coding..!