I tried replicating the paint from sweden that give this beautiful Red color to their house (Falu red on Wikipedia) with material I could source easily.
By following the recipe you will get a nice red paint that is fungicide, should last 10 years and the color is stable to the UV. It works well for wood but I don't think it will work with concrete or plaster.
(When I said Non Toxic, I mean that will not kill you like lead or chrome oxyde. But try not to swallow it please)
On the left picture you can see some brown paint made with a brown iron oxyde and the blue one is a failed attempt of blue paint with copper sulfate as Dye. The red one in the middle is what you get if you follow the recipie with red Iron Oxyde (Fe2O3).
If you manage to make some other color (like green with copper oxyde for example) please tell me i'm very curious to see the possibilities. There is a lot of room left to experiment with. like instead of flour use corn starch or potato starch.
2.5 Kg of Iron oxyde (III) (Fe2O3)
Give it's red color to the paint. you may be able to replace it with another pigment
650 g of flour
It act as a binder
8 liter of Water
Normal tap water
250 g of Iron (II) sulfate (FeSO4)
act as a dye fixative
I painted a few sample to see how they behave in the sun and the rain over a week, I will try in the following weeks to make more of it and paint the wood wall of my garden. In the meantime I will try to get some blue with prusse blue insteand of copper sulfate
Gather the material as lister above, get a hot stove, a beaker or a cooking pot and a scale
put 7 liter of water to 100°C (until it start boilling) and while doing so add all the flour to another recipient where you will mix it with the liter of water left until you have an homogenous and sticky mixture. Once it's done you can add the flour mix to the boilling water and keep stirring that it do not precipitate for 15 minutes. Once done you can jump to the next step
adding the Dye
now you will add the Dye (Iron Oxyde), the Iron sulfate and the copper sulfate to the mix while you keep stirring for 15 more minutes