That is one tricky image. I see the 5 in it, but it does seem to be missing some pieces in the bottom and top left. I have no idea how to make a '2' of this image though.
These images are often designed to diagnose typical forms of colorblindness though. The most common ones involve a big failure in the green or sometimes red sensitve cones, which are not uncommon in men. Such conditions are often noticed in early childhood though, and well documented too.
More interesting are the subtle mutations in pigments, that do allow people to see trichromatically, but with a bit of a twist. Color vision can then be decreased in part of the spectrum, but improved in another.
Those more nuanced differences are not studied often though, as individuals experiencing them have no problem functioning normally in most capacities. Tetrachromacity in women is something that is usually completely ignored in research, even though it is a real phenomenon... its just not a medical condition since people 'suffering' from it tend to have superior rather than inferior color discriminating capacities.