Maybe this is too simple...maybe I'm missing something...you don't need to measure 4 balls at once on 2 scales...
I'd keep it more simple since all light balls weigh the same and all heavy balls weigh the same.
1) Weigh one white ball and one white ball - one on each scale.
- we find out the weight of the light ball
- we find out the weight of the heavy ball
2) Weigh one red ball and one blue ball one on each scale.
- we find out the red ball is heavy or light.
- the other red ball is the opposite
- we find out the blue ball is heavy or light.
- the other blue ball is the opposite
This does not consider the case where your second weighing has equilibrium. Then you don't know if they're heavy or light, just that they're the same.