Pen seems to be always transparent? [Resolved]

The pen is seemingly transparent, despite the fact that I'm setting its transparency to 0.
Use the lightbulb to toggle the color of the background, causing the frame to change colors (showing its transparency)

I've exported an isolated version of my project showing this behavior here:
https://snap.berkeley.edu/snap/snap.html#present:Username=yna2jd&ProjectName=Transparent%20Pen

Try setting the pen size to 2, I don't know why but drawing a square with pen size 1 results in tiny gaps between lines, making it look transparent.

Much appreciated! This solved a few other strange bugs I was encountering too. Seems 2 is the way to go in general