With this combo, you either love it, or you don’t! It such a hit or miss combination but I have concluded there really is no correct way to do denim on denim, but there is a safer way. I would not really venture into colours in different families such as red and blue (well I could but I would rather not).
I think the safest bet with denim is matching in the same family such as blue and blue or with neutral colours such as blue with black or blue with white.
Clearly my favourite remains blue on blue. What’s yours?