Question: is it impossible for a girl to be colorblind

Answer: No, The most common cause of color blindness is an inherited problem in the development of one or more of the three sets of color sensing cones in the eye. Males are more likely to be color blind than females, as the genes responsible for the most common forms of color blindness are on the X chromosome. As females have two X chromosomes, a defect in one is typically compensated for by the other, while males only have one X chromosome. Color blindness can also result from physical or chemical damage to the eye, optic nerve or parts of the brain. Diagnosis is typically with the Ishihara color test; however, a number of other testing methods also exist.