The X chromosome (Xc) contains the faulty gene that causes color deficiencies.
Because males only have one X chromosome, this abnormal gene will always be expressed, resulting in color deficiency in a male (with XY chromosomes).
On the other hand, females may carry the gene for color blindness yet still have normal color vision. Females have two X chromosomes (XX), which accounts for this.
As long as a female has one normal X chromosome, she will have good color vision because the normal allele for color vision predominates over the defective allele.