why cant a male with normal vision be a carrier of the allele for color blindness?

Bad question.

1. Blue-yellow colorblindness is autosomal. The author of the question should have confined the scope to red-green colorblindness which is sex-linked on the X chromosome.

2. A Kleinfelter syndrome (47,XXY) male can be a carrier of red-green colorblindness. The author of the question should have specified normal male with normal vision.

Note: Kleinfelter males have reduced fertility but there are treatment options.

the allele for color blindness is on the X-chromosome and males have only one X (are XY)