The point is. I define and check the visualization in Qgis, and then I want to export the results to be served as a OpenLayers Vectorlayer, or as a Mapserver layer. Of course, with the color defined in Qgis.
Openlayers and Mapserver give the option to read the color from an attribute value (here and here). Maybe there is an easier way, but in this case I developed a small plugin to export the current visualized color into a specific layer attribute.