Home-made flour based paint that will last 5+ years outside. Nontoxic and cheap. Heat an old pot, pour in 300g flour and 300ml water when begins to heat, pour in 3 liters of water and stir (like a white sauce), and boil for 10 minutes then add 600g of pigment and linseed oil 300ml, bring to a boil for 30 minutes. Let cool down, it's ready, we made 3 liters of paint.
Seriously?! -- Vinegar works as a wood stain when you add a metal object in the mix and let it sit in a glass container for a week. A handful of pennies will produce a beautiful pale Caribbean blue stain. A wad of steel wool will give you a rich reddish hue. A combination of tea and a metal object in vinegar will produce a black stain. Log this away for later.