Thanks for your feedback @alphabyte. And I hear you. We will add this feature at some point. Right now we’re focusing on making the targeting process easier. Once we’ve finished that we will implement various improvements to working with the style options, including instant CSS style previews generated with JavaScript.
I think alphabyte is referring to the speed the style changes happen.
After applying a new color value for instance, Microthemer sends a network request to update the external stylesheet. Once this happens, the new stylesheet is reloaded and the style change becomes visible. If your have a quick network connection, or you are working on localhost, this happens pretty quickly, but not instantly. If the styles were updated by JavaScript however, the visual changes would appear instantaneously, without the need for a network connection.
Instantaneous is better than quick, which is why we will add this feature in future.