For changing the controls to match the Humanity theme, I copied: /usr/share/themes/Ambiant-MATEto:~/.themes/Ambiant-MATE
Then inside these files:
gtk-3.0/gtk-main.css
gtk-3.0/settings.ini
gtk-2.0/gtkrc
Replace #87A752(Ubuntu MATE’s green) with #F17949(Ubuntu’s Orange), and re-log in for changes to take effect.
Alternatively, you could make the changes directly to /usr/share/themes/Ambiant-MATE so they apply for all users, but beware if these changes are reverted later due to updates/upgrades.
Just as reference:
Ubuntu’s original “brown” theme is in human-theme and human-icon-theme.
Ubuntu’s current Ambiance and Radiance theme is in light-themes.
Applying the original Ambiance or Radiance theme directly in Ubuntu MATE will cause white panels / black text on the panels.