A new feature coming in 1.4 is the ability to finally turn your companion's helmet off and the ability to unify your companion's gear color. You're no longer required to have female companions hiding behind masks, or any companions wearing bad taste color combinations.
Pressing C ingame will bring up your character screen. Then simply select your companion tab and your options will show, as you can see in these screenshots.
You can unify the color of all, or selected items, the same way that you can with your main characters.