Why are Colloids Heterogeneous?

I understand that the definition of a heterogeneous mixture is a mixture in which 2 or more phases are present, i.e. you can see the mixture is not uniform. I know a homogeneous mixture is a mixture in which only one visible phase is present, but why are suspensions and colloids considered heterogeneous, for you only see one phase as the definition states? I also know that homogeneous mixtures are usually referred to as solutions, but if only solutions are homogeneous then why do we define homogeneous as anything with 1 phase; isn't this misleading? Is there a more accurate definition of a homogeneous and heterogeneous mixtures?

• You're taking "see" a bit too literately. For example milk has suspended fat globules which you can't "see" with your naked eye.
– MaxW
Sep 4 '18 at 19:57
• A solution of table salt (or any other low Mw solute) in water is surely homogeneous, because all inhomogeneieties have a similar (on a log scale) size and diffusion coefficient as the solvent molecules. For a polymer solution, you have to stretch this definition quite a bit already. For a colloidal solution even more.
– Karl
Sep 4 '18 at 20:27