Is coffee homogenous?
If you mean the finished drink, then strictly speaking no, its heterogeneous.
If you consider the finished drink, then black coffee probably seems homogenous, and indeed much of it is composed of water and compounds that are water soluble, but it does also contain small amounts of terpenoids such as cafestol which are not water soluble, and therefore make black coffee a very dilute dispersion. Dispersions by their very nature are chemically heterogeneous as the dispersed and continuous phases are not of the same state.
White coffee is certainly heterogeneous as it contains milk, which is a colloidal dispersion of fat droplets in water. This comprises two immiscible liquid phases, so is also heterogeneous making white coffee heterogeneous too.