Hmm... not with standard SLD... if I had to do it, I'd probably write a rendering trasnformation that splits the geometry collection into N features, one per sub-geometry, allowing each to be styled separately (it's not there, needs to be written)
Thanks @aaime , that sounds interesting. Is there any guide how rendering transformation works? I only find some old docs about the approaches: http://old.geotools.org/Rendering-transformations_191299715.html
the idea is to avoid allocating the entire collection in memory, which can be a GeoServer killer
I currently only use Geotools without Geoserver but I know what you mean... I also had these concerns.