[Beans]

I'm aware that the copper is reduced from Cu(ii) to Cu(i) to give the colour change from blue to red. But what accounts for other colours such as green or yellow. How does the concentration affect this?

[Corribus]

Copper I oxide precipitates and the color changes as a function of particle size.

https://pubs.acs.org/doi/10.1021/acs.jchemed.5b00563