This is similar to Microsoft Paint. Paint by choosing a colour and drawing. Use the in-game cursor to use the color palette, not the mouse cursor. Press R or C to reset. The mouse cursor is from macOS 10.11 El Capitan.
The cursor cannot be placed in line with the mouse cursor due to a bug in the Scratch Editor. You need to select the color using the in-game cursor. I'll be soon making an improved version of this project with more features and a better user interface. Wait for it, coming soon! Remix this if you wish to. The name is based on mspaint.exe (Microsoft Paint).