Click on the colour preview box (the one at the bottom-right corner) to change the colour selection mode. The rest is kind of similar to the Scratch paint editor, so it shouldn't be too hard to figure it out. Colour selection: either [red, green, blue] or [colour, saturation, brightness] like in the Scratch Editor.
the sliders are not drawn using pen If this lags, try running it on https://turbowarp.org/579312169
