Transparency?

[Suffice]

A quick look at the cheat sheet says to press T for transparency.

I tried this, but I'm not sure if I'm doing it correctly or even if it is meant to do do what I think it should.

Side note:
Transparency could also be an alternative to layers: #148
Just edit the the layers in another program.

Another suggestion:
A way to adjust the opacity of the reference images and and option to export as a PNG with the reference image as a background? Right now I'm just taking screenshots but the font is a little hard to read.