Google Maps JavaScript API won't display markers from KML exported from My Maps
There seems to be a bug.
When I remove the <color/> from
Style#icon-503-DB4436-nodesc-normal>IconStyle I see the marker.
According to the documentation <color/> isn't supported at all for <IconStyle/> and will be ignored, so it shouldn't affect the rendering.
Related: Issue 8551 in the issue tracker