The three layers all have the same contrast. It is the difference in sensitivities to blue and green light that allow contrast control. Have a look at Ilford's tech pub for a good explanation:

http://www.ilfordphoto.com/Webfiles/...8932591755.pdf

I used to make the same mistake myself (as I suspect most people do) when explaining how VC papers work. Somewhere along the way (I don't remember how) we all got the notion VC paper worked by having a green-sensitive low contrast emulsion and a blue-sensitive high contrast emulsion. In fact this is not the case.