You can go through each icon directly or do the whole set at once but it definitely will have issues and your computer needs to have some power. I went through each of the the folders and ran different batch processes through GIMP and used Geany to adjust fills with the .svg but I imagine any editor will do, Geany just has handy built-in colour tools. I also checked each as it came out the other end to watch for inconsistencies. The gray set is remarkably suited for this as it is a basic absence of colour making it really easy to get the exact colour you want. It is still a no-good dirty cheat but variety is the spice of life. With the Gnome set it is more detailed and far more time-consuming.