With the standard Font Awesome icon for YouTube (which is the icon font source that Joomla uses), it's a play button which is in a single colour only and the triangle in the middle is actually transparent and you still can see through to the image underneath.

Is it possible to have something like a small white square behind it that is then covered over by the play button icon? It would mean that the triangle in the (YouTube icon) button is white instead of being transparent and this would be so much better.

This would be great if we could do that. Definitely worth the customisation.