Theemo can apply transform operations to color variables, currently to change hue, saturation, lightness and opacity.
Well, actually due to plugin limitations, this can only be done on styles, instead of variables. In order to do so Theemo maps your references from variables to styles, applies the transforms on the styles and pushes back the value to the variable. That is in variables you stop seeing the reference, which becomes visible in Theemo. Here is a sample:
Keep Theemo open to have your values auto-updated.
It's quite helpful in building automatic color palettes.