The choice of colours wasn’t great and there wasn’t a “more colours” button. After a few minutes of growling I went to Tools -> Options … and clicked on the colours menu item. Lo, and behold.
Not only can you add colours but you can completely alter the available colours for the grid. I can imagine this being a really useful tool for adding presets to assist with corporate branding or other situations where continuity is important and you don’t want to pick a non-corporate shade of green at any point when creating a document!
That’s my nice-software-touch of the week, what’s yours?
1 Dia is my diagramming program. Its interface is great, but its unlike anything else so expect to have to work at using it to start with.