If a child seems to have any confusion with colours, colour vision should be examined carefully. We have two eyes but see only one picture, image . Visual information coming from the two eyes is fused into one image in the visual cortex . Not all normally sighted have binocular vision . They do not use both eyes simultaneously, together.
Some persons look alternatingly with their right or left eye.
They are usually unaware that they use their eyes separately. It does not disturb them. Stereovision or three dimensional vision means that we have depth perception in near vision. When we look far away we have another kind of depth perception. We pay attention to the relative size of objects and which object is partially hidden behind another object.