In some situations, rather than use sliders, I have actually mixed the color I needed to paint with on the canvas. This technique is similar to the way an artist would use a palette to mix paints together before painting with them. Generally, the way to do this is to find somewhere in the corner of your painting or on a blank layer and paint colors over the top of each other with varying levels of opacity. The lowering of opacity will lead to the colors blending together on the canvas—meaning that you can then use the Eyedropper to sample the color that you need. Typically you then use the undo button to remove the mixing or delete the layer containing it. If you are using ArtRage, ProCreate, or ArtStudio, there are paint options for blending colors together that are already on the canvas. In ArtRage there is a palette knife tool, in ProCreate you have a smudge tool, and in ArtStudio a Wet Paint Brush. All these tools give you the opportunity to 'smudge' the colors on your canvas into each other.