Using the plugin on Cygwin/Git Bash on Windows, with default settings, doesn't work - background color of indent guides doesn't appear, and still black in color.
After some tweaks, this is fixable with a line Term=xterm-256color in ~/.minttyrc. That setting will fix export TERM=xterm to export TERM=xterm-256color for vim's coloring to show properly.
I am adding this issue to suggest adding a note in your README about Windows mintty terminal. The note can mention that it is needed to set the terminal to 256 colors (its vim default to 8 colors with a dark background). Otherwise, the guides will likely not appear. The note will be good for in-experienced users.
Thank you.