A colloid contains particles of solid or liquid, or, bubbles of gas while these particles are suspended within a solid, liquid or gas, with the exception of gas colloid bubbles being suspended in a gas which is not possible. Colloids are either colored or translucent due to light reflecting on the particles within them. Some examples of colloids include pumice, gelatin, smoke, dust and milk of magnesia. The term colloidal suspension is referring to a substance that has a solid permanently suspended in a liquid.
In order to determine if a substance is a colloid or merely a solution you can check for Brownian movement, the constant motion of particles in solutions and colloids. This movement and its constancy are true of both substances yet if the substance is a colloid the particles will resist settling to the bottom. The particles in a colloidal suspension are a certain size which will typically be from ten to ten thousand angstroms. Another characteristic of the colloid is that the particles within its composition are not easily filtered or taken from the solution by any normal means.
Colloidal Solutions are heterogeneous mixes that have particles between the size of a true solutions and a suspension. Things that create smoke make a colloidal solution that consists of solid particles that float in air. Colloidal particles will pass through a filter paper but not through a parchment paper or the membrane of an animal.
Near in structure solutions such as true solutions and suspensions can be confused with colloidal solutions. That is why it is important to understand the differences between these various substances. Before you have colloidal solutions you have true solutions. True solutions are homogeneous, true solutions have no Tyndall effect, true solutions have particles that are not visible by the naked human eye and the particles within a true solution can pass through filter paper. The Tyndall effect is the occurrence of light scattering within a solution. Colloidal solutions exhibit this effect. After colloidal solutions you have suspensions. Suspensions cannot pass through any papers or filters and possibly display a Tyndall effect, yet may be void of it. A suspension is also opaque in color and it is heterogeneous.
The term heterogeneous, as in the colloidal solutions, means that the substance or parts of it are not uniform while when something is homogenous it is uniformly structured. You can see from the above explanations that out of all suspensions the true solution is the only one that is homogenous or uniform in the size of its particles.