In short, no there is no way around this (AFAIK, at least).

Guards are macros that are run at compile time, this is why you need to import them (you could also require them if you wanted). Compile-time pretty much boils down to “inside the module’s body” though also applies to guards: the block given to when is evaluated at compile time only, as opposed to the block given to do which is evaluated at runtime. This is why the scoping trick won’t work as the import inside the function’s body is checked at runtime.

Finally, the reason you can’t rename functions on import is because import doesn’t work like I’m assuming you think it does. It doesn’t “bring functions into a module” it really just “opens up its scope for function resolution,” hence the name “remote” function. When you do import Foo, only: [bar: 1] then call bar(), the compiler essentially rewrites it to Foo.bar(). I suppose function aliases could be a thing, though I never really thought of it

In any event, all that to say, an option would be to just require instead of import, then you can do:

defmodule Combined do
  require A
  require B

  defguard is_color_name(atom) when 
    A.is_color_name_from_A(atom) or
    B.is_color_name_from_B(atom)
end

EDIT: Oh, @hauleth beat me to the same advice I just shouldn’t have been so wordy