Marker meshes are white in Rviz

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I am including a mesh in .stl format as Marker in Rviz. Even if I manually set the color of the Marker and set the .mesh_use_embedded_color flag to false (which should not even be a problem, since .stl have no color), the marker is still white. The funny thing is that sometimes it is gray (as I set it to be, r=.4, g=.4, b=.4, a=1), but most of the times it is white. This thing is driving me crazy.

I know there are many other posts on this problem, but still I could not find a solution.