ImageAlpha

I thought there was a function to make an image semi-transparent. Is there one and what is it?

In 2D, there probably is one in the code archives. Probably be a bit slow for real time use though. What you can do, if the resolution is high enough, is checker your image with the mask colour, so it looks semi transparent ;)

Or paste it to a sprite which covers tha camera, the use EntityAlpha to fade.
There's something in the last couple of pages of this forum about just that.