For the program Paint Pot, I chose a colorless rainbow as my background.

I then created three buttons, with the color designation and in my block editor , made them red, blue and green. When those buttons are clicked, you then select that color to draw on your image/canvas. After when you click, it will start with a radius of 5 and give you a dot. If you then drag it, it will draw a line of that color of the button you selected.

Finally, you can erase what was drawn on the canvas and restore it to the original picture.

This is the block editor for PaintPot