[thaumasiotes]

> So is it possible that in the distant past, a civilization would consider dark red and dark blue the same color? That instead of one "blue" category they would mix several other unnamed colors?

> I can believe it.

Different cultures divide the color space differently, but they don't lay it out differently. For a civilization to consider dark red and dark blue to be the same color, those colors would need to show similar activation profiles, both for blue-yellow cones and for red-green cones.

[Iv]

Or they would have to attribute more importance to luminosity than hue. In the absence of artificial light, low-light vision is much more important than differences in color as humans would spend a huge part of their awaken time in luminosity insufficient to discern colors.

[thaumasiotes]

In the absence of artificial light, people mostly sleep when it's dark.