‘Swedish paint’ or ‘Flour paint’ is environmentally friendly, cost-effective,
and durable: it has been used for many years in Scandinavia for houses, fences, and other outdoor buildings. The paint can actually be made in a really short time, this recipe will make 3 litre of flour paint:

300 grams of basic flour
3 litres of water
600 grams of pigment
300 millilitres of linseed oil

Use an old pot: put it on the stove and heat with 300 g of flour. As it starts to warm, gradually add 3 litres of water, stirring as you add. Bring to a boil and let it boil for 10 minutes: it will thicken.
Add your pigment of choice and 300 ml linseed oil. Bring back to a boil and let boil for 30 minutes. When time is up, let it cool: you now have paint. You can add a little black soap for texture. You could even add iron sulphate if you are using it outdoors: it will add resistance against moss.

Don’t forget to properly prep your wood surface before applying paint: this means removing existing paint or stain and sanding coarsely. Once you are finished painting, it should be dry in about 1 hour if painting at 20 degrees Celsius (or 68 Fahrenheit). Clean your brushes with water: no heavy cleansers are needed, no awful paint smell. You can get pigments at DIY stores.