[jessaustin]

I would suggest just white (or whatever the background color happens to be), with a dashed border.

[jessaustin]

Now that I've seen the update, I think just make it transparent, so it is the color of the button on which it is placed. The dashed border is nice though.

[sharkdp]

Thanks for the feedback! The dashed border was a really good suggestion. I like white better than 'transparent', though.