A colloidal solution has two main components. They are the colloidal particles and the dispersing medium. A key feature, which distinguishes colloids from suspensions is that a colloidal solution never settles. The particles will always remain suspended.
Colloidal solution exhibits a property called the Brownian movement. The particles have a random, zig zag motion, when observed under the microscope. This is due to collisions between the particles in the dispersing medium.
When a beam of light is shone on to a colloidal solution, the particles on the path of the light will be illuminated. For examples, on a foggy night, the path of light from a car head light can be seen.