In substitution type of questions, some particular objects are assigned code names. Then a question is asked that is to be answered in the code language.
If white is called blue, blue is called red, red is called yellow, yellow is called green, green is called black, black is called violet and violet is called orange, what would be the colour of human blood ?
The colour of the human blood is 'red' ans as given, 'red' is called 'yellow'.
So, the colour of human blood is 'yellow'.