GPX/WKT line color changing to black when non-default marker color is selected

I use OpenLayers to show my trekking data. I have successfully created a content type with a File field to download a GPX file and a Geocoded field to get the data from that file into a linestring, and a map containing a Placeholder for Geofield Formatter layer on top of e.g. Google Maps layer, to show my data. When I leave the default color selection in Layers & Styles for that map, the line (as well as the markers, if any) is shown on the map in dark-yellow (see e.g. http://personal.kozub.in.ua/test-trek-1, http://personal.kozub.in.ua/test-trek-2). However, if I select e.g. "Marker Red", the markers (if any) become red indeed, but the trek line becomes black.

I am not sure whether this is a bug, but if OL does it by design, it is worth describing somewhere in the documentation.