Keyboard Shortcuts?

Let me start with something quite basic. Here are three patches of colour. The patches are all different colours, but the two leftmost are both the same colour---they are both blue. This sounds contradictory but isn't. In one case we're talking about the particular colours of things; in the other case we're talking about colour category.

The question I want to ask about knowledge of colour concerns these cateories. You know that these two are both blue whereas this is not (it's green). How do you come to know this? (Ask them to discuss.) Does anyone thing the answer is that you can just see it? As we'll see, that idea looks promising initiall but it's not quite that simple.

*TODO*: \citep{webster:2012_color} has good summary and lots of complications about CP. Also introduces methods not considered here.