I am using the Kanji Colorizer add-on to generate stroke order diagrams for the kanji I am learning. Recently I wanted to convert all the colorful diagrams to simple black and white diagrams for design considerations. Rather than tweaking the source code of the add-on, this can be achieved with the simple sed command (to be executed in the media dir), which replaces all colors in all .svg files with black (this cannot be undone, so make sure this is what you want!):

for file in *.svg; do sed -i -e "s/#[0-9a-f][0-9a-f]*/#ff0000/g" $file; done