diff --git a/src/engine/engine_vis_visualize.c b/src/engine/engine_vis_visualize.c
index 02491e44..b8a479f2 100644
--- a/src/engine/engine_vis_visualize.c
+++ b/src/engine/engine_vis_visualize.c
@@ -910,6 +910,10 @@ void mjv_addGeoms(const mjModel* m, mjData* d, const mjvOption* vopt,
               }
             }
 
+            if (rgba[0]==0 && rgba[1]==0 && rgba[2]==0) {
+              rgba[3] = .1;
+            }
+
             // draw triangles, one per side
             START
             makeTriangle(thisgeom, pos[0], pos[1], pos[2], rgba);