How we perceive colours varies greatly from one person to another. Generally, we can all identify the primary colours such as Red, Blue and Yellow. The human eye can generally pick up these colours but for some Red could be identified as Blue.
The reason for this may be due to colour blindness. More commonly it is due to the colour sensitive receptors of the eye called melanopsin. Scientists discovered that the amount of blue or yellow incoming light can greatly affect the way we perceive certain colours. Interestingly, the human eye is incapable of seeing the colour Red-Green (not brown) and Blue-Yellow. This is because these colours contain light frequencies that cancel each other out and make it impossible for the human eye to visualize.