Square or not, that's really beautiful :)

It's possible you have an effect in the Whole Drawing category. In this map I have an RGB Matrix Process turning the entire map grey

To check your own map click the Whole Drawing radio button at the top of the effects panel. Anything there will affect the entire map.

When I'm not so busy I will have a look at making a small set of backgrounds, maybe as an annual issue, though it would have to be impressive enough to become that.

Time well spent. It's beautiful :)

Off the top of my head I can't say for sure if the Wilbur colour schemes were included with it or not, but they aren't critical for carrying out the procedure unless you particularly want to print a result from Wilbur in one of the available colour schemes. You can still erode your world in Wilbur without using any of them, and you can spend hours of fun making your own as well.

A word about that hours of recolouring the CC3 map. There is a way of doing it much faster than that was developed by André Frank shortly after the publication of the original annual. This blog explains it and provides the necessary colour palettes:

https://rpgmaps.profantasy.com/exporting-coloured-topographical-maps-from-ft3-to-cc3by-andre-franke/