Powertex Bister Swatches
Now this one may seem obvious, but you would be surprised. In workshops where I give a choice of colour I always like to have a swatch of each of the colours, to give myself and my students a chance to visualize what colours may look like together.
These swatches are Powertex Bister over Powertex Stone Art. I deliberately made the Bister more dilute and got the students to build the depth of colour up in layers ( drying between layers).
Hope this may be of use to someone. It saves me both time and products as the colour choice is made without actually using any product.