It wasn't that complicated, just very time consuming (and I mean a very!) going through the svg files in the UI folder and individually opening, changing the grey colours to another colour, then saving them in Inkscape. As they are not labelled ideally either, they are all just numbered, you have to go through practically all of them too. I backed up the folder of svg files first and then pretty much went playing. The results aren't perfect either, because it seems some of the svg files are layered and I couldn't access the colours underneath parts of some of the designs properly. Whether that is a limitation of either me or Inkscape I don't know. Maybe Illustrator would be better, but for me Inkscape was free, and it was the first time I'd ever used it, so I can live with the limitations. To be honest, it is pretty much a pointless excercise, but I always liked that in previous versions an interface colour change was always fairly easy, and now I can do it in later versions.