Notice how the masthead at the top looks a different colour, but isn’t darkened like in the Protanope.
Ishihara Colour Vision testing simulation
This is a simulation of the most severe form of a green defect, some with a very mild defect would see the site almost the same as a colour normal.
These are only simulations! Your monitor calibration, room lighting and own colour vision will affect what you see, but it does give a fair simulation.