Instructions
Enter the "Appearance" option from the Settings menu. This option allows you to change many aspects of your online Spartan or Elite character's look.
Scroll down to "Colors" and press A.
Pick the shades of green that you want for your character's primary, secondary and detail armor colors. The three hues of green available to choose from are "Sage," "Green" and "Olive." Press the A button to confirm each color selection.
Exit the Colors menu by pressing B once you have saved your preferences.