Color blindness is added the majority will say that a match has been achieved. Finally, as yet more red is added, the remaining, protanomalous, observers will declare a match at a point where normal observers will see the mixed light as definitely reddish. Protanopia, deuteranopia, protanomaly, and deuteranomaly are commonly inherited forms of red-green color blindness which affect a substantial portion of the human population. Those affected have difficulty with discriminating red and green hues due to the absence or mutation of the red or green retinal photoreceptors. It is sex-linked: genetic red-green color blindness affects males much more often than females,
Colour cast Improper timing or imbalanced chemical mixtures can cause unwanted casts. Colour casts can also occur in old photographs due to fading of dyes, particularly under the action of ultra violet light. These may be correctable on a scanned version of the photograph with image editing techniques. Most digital cameras try to automatically detect and compensate colour cast and usually have a selection of manually set white balance settings to choose from. Otherwise, photo editing programs, such as Photoshop, often have built in colour correction facilities. For film, blue filters and amber filters are used to counter casts. Amber filters are