And this is where things took a turn for ...beetroot ink! (I was a bit bored of watercolours).
I guess it still counts as a primary colour :)
I love beetroot ink! This is not the first time I used it, although I mostly did lettering before: I had a poster professing my love for beetroot in my kitchen, right next to my caffeinated poster about (surprisingly!) coffee.
I don't know a lot about how well it holds over time. The wall in my kitchen was never hit by direct sunlight and when I moved I just filed the illustrations away in dry and dark places (😋) so they still look good after all this time, but I wouldn't do a professional illustration using this home made ink.
FYI: chopped up beetroot, covered with water, a few rounds in the microwave on high power, strained it through a paper filter, one teaspoon of vinegar..et voilà!