The problem with perspective styles vs variables is that styles require you to apply the color to something. So if I want to use the same color for a text, for a background, for a border, and whatever else, I'll need to make as many styles, instead of just using that variable. It's frustrating.
Instead, I use the method @bmusson described in the css thread a while ago, with variable indirection, in the stylesheet or theme files. Then I create empty perspective styles with the same names to make them easily selectable.
For one of a kind stuff, I still use the variable directly in the properties. It's somewhat buggy in the designer, as it doesn't update systematically, but I don't mind.