This doesn't mean that greens are invisible to people with deuteranopia.
Human vision is complicated.
The role of the green cones is less to detect green light than to distinguish it from red. This figure simulates the web-safe colors as they appear in a deuteranopic condition. In most other categories of color blindness, protanopia, protoanomaly and deuteranomaly, the view is very similar but there are subtle differences. In one very rare form, called tritanopia, affecting thirty people in a million, colors appear very differently. The BT Labs site excels at explaining and illustrating these points.