If a bluer blue-green is required, what should be increased in the mixture?

Correct answer: Blue

The governing concept is proportional colour mixing. Blue-green is produced from blue and green; increasing the blue component shifts the mixture toward a cooler, bluer green. Therefore option B is correct. Increasing yellow would make the mixture yellower, red would alter it toward a duller or warmer tone, and white would lighten the value rather than make the hue bluer.