How to unlock new color
Moving to players helping players.
You unlock new hero colors by buying or acquiring items that have that color
The new color on your screenshot, for example, in from the new set on Pro-Shop:
If you get any of those items you unlock their color for your hero
the color is unlock by the color of a item. Example you unlock red by get the Purgatory uber. Get green by take a Uber with green color,etc… So to unlock a specific color you need to find a item with the color. So for the white you need to find a item who is white and so on