Comment by ivanhoe

I'd say it should be rephrased as "could only name a color as categorically distinct from others" to make it more obvious. If you're asked if something is blue or red, then turquoise would definitely be described as blue, but green also. It's not that you wouldn't see the difference between sky and grass, it's just that you'd classify it all as a different shades of the same color, as it's closer to it than to say red. On the other hand yellow would probably be a shade of light red in that example. Once you're used to that palette you'd start simply ignoring the differences in shade for practical usages, like for instance Cambridge Blue is called blue, while to me it's really green.