"orange_(color)" is cumbersome to type, with its parentheses (shift+9, shift+0) and whatnot. I discovered this when I was fixing some orange-colored images mistagged orange, which is for the fruit.
It has the same number of letters as, but more keystrokes than, zettai_ryouiki, whose helpful shortcut is /zr.
In fact, if orange_color was the main tag name, that would help and look good, too. Frankly, both it and orange_(color) look weird for being obvious disambiguations from orange (fruit), while "orange color" sounds natural enough in English phrases.
Updated by jxh2154