Changing vim 'gutter' color

To change the color in your ~/.vimrc so that your gutter is the same color as where your line numbers show up is the following:

highlight clear SignColumn

The git-gutter docs have some other helpful suggestions.

This "gutter" is called the signs column. (See :help signs for more information.) The highlight group associated with this column is called SignColumn, and can be set like this (using the example from the help section):

:highlight SignColumn guibg=darkgrey

Another option that hasn't been mentioned is to eliminate the sign column entirely and put the signs into the number column.

Adding this to your ~/.vimrc

set signcolumn=number

produces

(this is using custom symbols with the Ale plugin in iterm Vim).

This is available in "full" Vim versions 7.4.2201 or newer that include the +signs feature (I use the version installed by Homebrew on MacOS).