[Settings] Add strings for Natural and Automatic color modes

These strings are not properly reflected in the UI yet.  Automatic and
Saturated currently map to the same display setting (and the UI reflects
this by checking both).

Bug: 75982435
Test: Modified the existing testcases to reflect the new string.
Change-Id: Iaef08599c0233e018eaafaf89d60eab92e102782