add particle of a different color

MD/pyMD_rigid.py

@@ -82,9 +82,15 @@ pos = grid (N, bl, W-2*sep, H-2*sep)
 
 ## Add molecules ot the scene
 molecules = []
+i = 0;
 for p in pos:
   molecule            = ball(p, radius)
-  molecule.color      = Color('red')
+  if i==0:
+    molecule.color      = Color('blue')
+    i +=1
+  else:
+    molecule.color      = Color('red')
+
   molecule.elasticity = 1.0
   molecule.friction   = 0.0
   molecule.gravity    = (0.0,0.0)