How to Do a Black and White Partial Color Effect with The GIMP

With the grayscale layer selected, go to the Colors menu and choose Desaturate. The remove colors dialog offers three ways of converting to grayscale. You can experiment with these to see which one you prefer. For this photo, I am going to use the Luminosity option. Press the Desaturate button after making your selection. Undo and repeat the command using the other options if you'd like to try them out.