The yellow/blue cube in f102v2

[davidjackson]

I was reading up on sunstones, You are not allowed to view links. Register or Login to view., a polarising crystal used in the early middle ages as a navigational device ; you can use them to determine the solar azimuth even on very over cast days. Abulafia explains how the Nordic people used them. From Wikipedia :

Research in 2011 by Ropars confirms that one can identify the direction of the sun to within a few degrees in both cloudy and twilight conditions using Iceland spar and the naked eye. The process involves moving the stone across the visual field to reveal a yellow entoptic pattern on the fovea of the eye. Alternatively, a dot can be placed on top of the crystal so that when you look at it from below, two dots appear, because the light is “depolarised” and fractured along different axes. The crystal can then be rotated until the two points have the same luminosity. The angle of the top face now gives the direction of the sun.

Which would explain the two 'eyes' in the blue cube. 
Of course, there is zero reason for a sun stone to be depicted amongst plants, but for some reason I immediately thought of the blue cube.