Adefect in the what results in difficulty in visual detection of color and fine detail

A defect in the cones results in difficulty in visual detection of color and fine detail. 
Color vision deficiency represents a group of conditions that affect the perception of color. Red-green color vision defects are the most common form of color vision deficiency. Affected individuals have trouble distinguishing between some shades of red, yellow, and green. Blue-yellow distinguishing between some shades of blue and green and cause difficulty distinguishing dark blue from black. 

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Photo means light and synthesis means combination so combination of light