To change colour, just click on the letter that starts the colour. For example, to change it to purple click on p, or to change it to orange, click on o. The colours are: P for Purple O for orange B for blue G for green R for Red Y for Yellow I have not added pink yet, but if enough people ask for it in the comments, I will add it. To increase the size, press the up arrow and hold to carry on going up, but to go down it is the same principle apart from the fact that you press the down arrow. Also, press c to stop the pen and d to start it.
I did all of this on my own, but I thank Joetechman and Brickmon for the inspiration to start scratching. Enjoy! PS: 18odona and @Joetechman's games are AMAZING, so be sure to play them.