DIY 2 Ingredient Homemade Watercolor Recipe from Growing a Jeweled Rose. Really cheap and easy watercolors with ingredients you already have. Also, as mentioned in the post, you could use vineagar instead of water for added fizz.
DIY Stencil Art Using Watercolors and Dollar Store Stencils. Simple project for kids or anyone to make. Tutorial at Growing Creative here.
DIY Watercolor Eggs. Three different techniques using watercolors. Tutorial from Oh My! Creative here.