gitk will not start on Mac: unknown color name "lime"

I also found the same problem with exactly the same version of git and OSX. As a temporary workaround I suggest you to do the following:

cp /usr/local/bin/gitk /usr/local/bin/gitk.bkp
vi /usr/local/bin/gitk

and replace all occurences of lime to any color you want (I used #99FF00). Here is the vim command:

:%s/lime/"#99FF00"/g

EDIT: Please follow Keith B answer for permanent fix.

@Konrad Thanks for the help!! Although the answer is correct, please be aware that your command

:%s/lime/"#99FF00”/g

contains two different quotation marks, which will def. throw an error if copied & pasted.

So in order to go through with it, I had to do:

cp /usr/local/bin/gitk /usr/local/bin/gitk.bkp
vi /usr/local/bin/gitk

And inside vim:

:%s/lime/"#99FF00"/g

You can check your version of Tcl/Tk by running wish and using the command info patchlevel. It appears that git 2.7.0, Tcl/Tk 8.5.9, and OS X 10.11 El Capitan do not work well together.

I solved this problem by doing brew cask install tcl, which installed 8.6.4, and gitk works now.

If you don't want to use Caskroom, follow this:

$ brew install tcl-tk
$ brew link tcl-tk --force