In a report on an open-source separation kernel (Muen kernel) I was reading, in the future work section, it says that cache coloring can be implemented to prevent covert/side-channel attacks.

It is mentioned that

In a second step each subject is associated with a color. All subjects of a given color share the same cache partition. In turn subjects of differing color have no access to identical cache locations, which means the cache cannot be used as a side-channel.

I understand what page coloring/cache partitioning is, but I do not understand how having different subjects use different cache partitions can solve side-channel attacks. Can anyone enlighten me on this?