Multiple Versions of one Module in same Environment

[Sukera]

Pkg can't load packages present in Manifest.toml?

You can only have one version of a given package at a time. You can, however, have different packages with the same name in the overall dependency graph. It is intentional that you must explicitly declare your dependencies at the top level. These are connected facts since the top-level Colors could be totally unrelated to an indirect Colors dependency.

The workaround, as noted in that thread, is to fix one of the packages.