Eeer... Thanks... But I am not sure that's the whole story.
The red hitbox is what causes damages. When it appears, it does not replaces the 2 others. Damages are probably applied when the red collides with of the 2 other. But which ? And what does the other do ?
In the patch notes I have found the two words "hitbox" and "hurtbox" which are probably 2 different things.
Also I noticed that the yellow box sometimes becomes blue or pink. It surely means something.