How to use the drawing tool to make a colored transparent rectangle?

I want to make a rectangle with a red outline and filled with a transparent blue color, but not sure how to do it.

Hi Nick! This does not appear to be possible using the new User Interface. This should be changed (I'll make a report). If you choose to use the old toolbar, you can do this by putting a transparency value as two additional digits in the color definition. These will be a hexadecimal pair, like the r, g, and b, channels, with 00 being fully transparent and ff being fully opaque:

Thanks! Weirdly using the new UI, I got a transparent fill on accident. No idea how it happened, but couldn't find a way to replicate it.