Add button to change subtitle color.

This PR creates a button on the control panel to change the subtitle color to Yellow.

I don't think that this change should be accepted as it is now. I created this PR to start a discussion on the best way to make it and share an issue that I found.

My initial ideia was to make this button a toggle that changes between white and yellow. The problem is that a click in any button on control bar is triggering the onClick twice, making it really hard to create a toggle. Any idea on why this is happening?