I use the brown terrains because I like how they look. I've also never bothered with learning the sticky patches for grenades. Nor do I have any trouble seeing flags/players. But I can see why other people would. I guess I just like seeing the shadows on the brown terrain.
I also came to the conclusion a long time ago that skins/configs don't really matter as much as people think. As long as you have decent fps and vsync disabled via gpu control panel, with enhanced mouse pointer turned off for windows, nothing is really game changing. I have consistently changed skins/configs/mouse sens/fov/resolution and I've always been the same player. Pft/terp can make a difference but I personally don't recommend setting terp to 0.
Comes down to pc hardware, desk setup, experience, natural talent, desire to be great, and an open mind willing to listen to others.