Another words, the mixture is uniform in its composition. Heterogeneous mixture have components that are NOT uniformly distributed throughout the mixture. Sometimes this distinction is quite visible like the pulp in orange juice or the rocks in concrete. Samples taken from different places in the mixture will be different and the ratio of one component to another will vary. The mixture is not uniform in its composition.
Homogenized milk is a good example of a colloid.
The droplets are too tiny for gravity to rise to the surface as a fat layer.