No, it's actually a good question, I know people who always play with specific colors even reserve/2nd if the first one is occupied, Im one of them.
In War3 my color of choice was
green my second color was
grey, if both are busy I would then go with
blue. That's how I've been playing war3 with others, green being the official.
Ever since I created my official full nickname in 2006 that I dont use on forums and my
LOGO (with actually light grey sphere not black like here) in 2008-9 I started using the colors of my logo, like teams in sports use the colors of their countries or team logos.
Since the logo includes these colors you see,
Blizzard blue became my main and official color, while second remained
grey and third became the former one i.e
green.
Since War3 had not even close color, I have been playing War3 in 2009-2010 (my last war3 years) with having replaced from the MPQ the green with
Luckily ever since SC2 came, it had a very close color especially in the game lobby, Teal, so of course it continued to be my official color when I play vs others on 1v1 tournaments, or training melee.
As SC2 has no grey among the chosen and Dark grey is too dark, I could use white as my 2nd color from the logo, Green remains my third.