I hold Ctrl and then hold and drag with LMB. Color is being spent and the game registers my drawings, but the mouse cursor doesn't make any lines. I just make empty movements with the mouse in the air and this happens with any color. This makes it almost unplayable since I have to guess if I'm doing the drawing correctly since I can't actually see it.

From what I've seen from other people playing it on Youtube the mouse cursor is clearly supposed to be leaving color trails every time I'm drawing which looks very pretty and it would suck to play the whole game without this.

I haven't seen anyone else report this bug anywhere and I'm really confused. Any suggestions on how to fix this?

Ok I figured it out. I had configured the game to run in windowed mode (wanted to play in borderless full screen) by editing "config.xml" in the data folder. This caused the game to have invisible drawings for some reason. Undoing this fixed it.