A rough 2D representation of sexuality
But it could be related more accurately to a 2-dimensional representation of a 3-dimensional color spectrum, relating colors to luminance and chromaticity:
The 1976 CIE Chromaticity Diagram
If you imagine that your "phylogenetic tree of sex" replaces the divisions with the color names shown on the field, then you can see what I'm talking about. The discrete parts of the phyla can be related in a generalizing way to the spectrum.
