Further collision beyond the OnCollisionEnter() event

I am creating a game where I need collision between blocks of the same colour to be acted upon. The blocks are c$$anonymous$$ldren of gameobjects w$$anonymous$$ch act to create clusters of blocks - kind of like Tetris shapes. The rigidbody component thus belongs to the parent gameobject and OnCollisionEnter is called only when two parents collide. I have no problem identifying when matc$$anonymous$$ng blocks collide when OnCollisionEnter is called. Here is the code I use for that:

 void OnCollisionEnter(Collision collision)
     {
         foreach (ContactPoint c in collision.contacts)
         {
             if ((c.t$$anonymous$$sCollider.renderer.material.color == c.otherCollider.renderer.material.color)
                 && (c.t$$anonymous$$sCollider.renderer.material.color != Color.gray)
                 && (c.otherCollider.renderer.material.color != Color.gray))
             {
                 ScorePoint = true;
                 c.t$$anonymous$$sCollider.renderer.material.color = Color.gray;
                 c.otherCollider.renderer.material.color = Color.gray;
             }
         }

(the blocks are coloured gray after colliding with the same colour)

The actual problem I have is illustrated below. In the first frame the gameobjects collide and no matc$$anonymous$$ng colours are detected. The collision between the gameobjects holds until two matc$$anonymous$$ng coloured blocks are touc$$anonymous$$ng, but of course OnCollisionEnter will not be called. I have tried playing with the OnCollisionStay event but I haven't managed to do so without raising huge performance issues on mobile devices.

If anyone has any advice it would be greatly appreciated. Perhaps a solution w$$anonymous$$ch works only in t$$anonymous$$s special case where all the individual blocks are cubes?