[R-sig-Geo] Plotting 2 rasters over each other on a map with 2D colour scheme

[Vasya Pupkin]

Hi guys,

What I am trying to do is to make a map that would show the areas which are hot-dry, hot-wet, cold-dry, cold-wet. I have 2 rasters with precipitation and temperature values. And I want to plot them over each other so that each extreme combination of the 2 variables (hot-dry, hot-wet, cold-dry, cold-wet) would have its own colour with respective gradients for the intermediate values on the colour scheme, that will have to produce a 2D colour legend. Below please see a link to the concept image, that I have produced for explanation. I saw such a thing once and thought that was a briliant idea to show how 2 variables interact, but then I totally forgot where it was. I have been googling for 2 days - no result. Any help is very much welcome - the name of the thing, name of the software to do it (how to do it would be marvelous), keywords to google, workarounds - anything.

Concept image:
https://cloud.mail.ru/public/SHno/98X3czaW5

Best wishes,
Vasya.