Stencil designed originally for my Dad so that he could more easily and quickly make James Gurneys Colour Triads. I have included the openscad file as the inner triangle on stencil 1 might need to be adjusted for your use and you can also create different sized triads if necesary. Change variable stencil1_inner_scale so that when Stencil 2 is drawn over Stencil 1 the drawn inner triangle of Stencil 1 meets the lines of Stencil 2. The scaling is necessary as the pencil can never track exactly on the edge of the stencil so tolerance is needed to allow for the pencil thickness.