Nn (male) x NN (female)
Gametes n (male) + N (female) x N + N

n (male) + N N (female) + N
| |
Nn (male) NN (female)

That is all offspring normal, but the males again heterozygous.

An affected male has the constitution _nn_, and if he marries a normal
woman the descent is as follows:--

nn (male) x NN (female)
Gametes n (male) + n (female) x N + N

n (male) + N N (female) + N
| |
nN (male) nN (female)

When a normal male is mated with a heterozygous _nN_ female we get

nN (male) x nN (female)
Gametes n (male) + N (female) x n + N
______________________|______________________
| | | |
nn (male) nN (male) nN (female) NN (female)

that is, half the sons are normal and half colour-blind, while half the
females are homozygous and normal, and the other half heterozygous and
normal.