If white is called blue, blue is called red, red is called yellow and yellow is called black. What would be the colour of human blood ?

The correct answer is (b).

If white is called blue, blue is called red, red is called yellow, and yellow is called black, then human blood would be called red. However, it would still be the same color as it is now, which is red.

The color of human blood is determined by the presence of hemoglobin, a protein that carries oxygen in the blood. Hemoglobin is red, so human blood is also red.

The other options are incorrect because they do not correspond to the given definition of the colors.