Is a colloid a homogeneous mixture?

Yes, under most circumstances we could consider a colloid to be a homogenous mixture, although it would not be exactly the same thing as a mixture that is entirely soluble, or homogenous at the molecular level.

A good example would be milk; milk is mostly water, which is polar. Mixed into the water are various proteins, fats and sugars. Fats, being nonpolar, are not soluble in water, and will tend to separate from the solution and form a layer on top after the milk is extracted: this is one of the first steps in processing dairy into cheese or other derivatives.

Because most of the "flavor" in milk lies in its fat content, it is often desirable to keep the fat evenly distributed. This also prevents the milk from spoiling as rapidly as it would in a separated state. However, because the fat and water are not soluble, it is necessary to force them into a mixed state, without chemically altering them. This is the process of homogenization; the milk is pushed through small tubes at high pressures, which smash the fat molecules into small clusters called micelles, and these micelles can dissolve in the water a little easier than large clumps of fat could. The resulting "solution" is a colloid.

So, from the broad scale, we could consider this colloid homogenous; every sip of milk should taste the same and have the same average solute-to-solvent ratio. However, at the molecular level, we would see that there are clear continuous regions of 100% water and 100% fat that are heterogenous at that scale.