What should be added to shift blue-green toward blue if it appears too green?

Correct answer: A small amount of blue

The governing concept is controlled colour mixing. Blue-green contains blue and green; if the mixture looks too green, adding a small amount of blue increases the blue proportion and shifts the appearance toward blue. Therefore option A is correct. Yellow would strengthen the greenish or warm tendency, while red or orange would introduce a different component and could make the mixture duller rather than bluer. Only a small amount should be added to avoid overshooting.