Colorblindness in females and random X chromosome inactivation
In heterozygote females with colour defect genes on the X-chromosome, even if approximately half of their photoreceptors are dysfunctional they usually have enough functional cone photoreceptors to have normal colour vision.

From Molecular genetics of colour vision deficiencies:


  Due to X-chromosome inactivation during early development,
  heterozygotes are mosaics for two populations of cones, one expressing
  visual pigment genes encoded by an X-chromosome that would cause
  colour vision defects in males, and the other expressing genes that
  would confer normal colour vision on a male. In support of this,
  patches of defective colour perception were detected by shining a very
  narrow beam of red or green light into the retinas of female
  heterozygotes for X-linked colour vision defects. The majority of
  heterozygote women (carriers of colour vision defects) have normal
  colour vision.


This means that  – in most cases – for a female to be colourblind, her father must be colourblind and her mother must be either a heterozygote (carrier) or homozygote colourblind. In a male, only the mother's X-chromosome determines whether he inherits the defective genes, so he is more likely to have the colourblind trait.