I know black and white aren't hues, but the logical place to put these new color options would be in another row added to the bottom of the power hue palate. You could leave the row partly empty, and potentially add other special color options later.
The new options could require a Zen store purchase to unlock. Obviously, you'd still need to be a gold player to actually set your powers to the newly-acquired "hue."
Black Power Pack: This would unlock the ability to turn the colored visuals of your powers black. So if you set Super Speed to this option, it would look exactly like Dark Speed. I'm sure this would be a big seller. You know how popular black is.
White Power Pack: This would unlock the ability to turn the colored visuals of your powers pure white. This is the one I'd personally be interested in. I really like the way the various Psi Holo costume pieces look when set to white. This would really open things up for matching powers to that.
Invisible Power Pack: This would unlock the ability to turn off the portion of your power's visuals that you would normally be able to color. For example, if you don't like the colored streaks that follow your weapon on certain attacks, you could turn it off. I think this one could turn out like Foxbat's Invisible Weapons, in that theme builders will probably go nuts for it.