It took me a while to figure this out but I was happy with the results and figured this might help someone else.  I had about 100 two color .png files that I wanted to change the color on.  I didn’t feel like editing each one by hand in an image editor so I stumbled on imagemagick.

I am on a Mac (OSX) so I installed it via brew:

➜  ~  brew install imagemagick
Warning: imagemagick-6.9.2-4 already installed
➜  ~

As you can see, I had already installed it. It was obvious, but here’s the command I eventually came up with:

convert filename.png -fuzz 25% -fill "#000000" -opaque "#4e9db3" filename_new.png

The infile is obvious. The “-fuzz 25%” seemed to make the entire replacement more thorough. If I went above 25% I found all the colors were replaced. The “-fill” tells imagemagick what you want to use as the replacement color. The “-opaque” is what you are replacing. To make it easier for me, I also outputted my altered file into a sub folder. Here’s how I looped through all the files:

for i in *.png : do
convert $i -fuzz 25% -fill "#000000" -opaque "#4e9db3" done/$i
done

And off it went. I was very happy with this result. You can read more about it here: Replacing Colors in an Image