I said on a different thread, I've noticed a correlation between hormone cycles and how I prefer to dress. Mid-cycle I want to wear attention getting power colors and then the rest of the time I want to fade into the woodwork. This is not really conscious -- though I have become aware that hormones are driving a lot of my fashion choices on a day to day basis.
Cobalt is the perfect example. My coat is cobalt, and I have a cobalt sweater dress, a cobalt satin formal dress, and a few other cobalt items. Now that you mention it, I do feel like it's THE Power Color in my closet right now. Everything else is more subtle and muted. The cobalt really stands out amid all the rest, when I open the closet door.
15 years ago, my Power Color was red - but it had to be a blue red/cranberry. The color of the coat that Aubergine just posted in her K/R. As I've aged, I've found that color a little more challenging to pull off, and I'm not sure why that is.
I wouldn't call it a Power Color per se, but one color that flatters me a lot is pink. Any shade of it, really, but the more blue-based the tone, the better. However, I own few pink items, and those I do own, are more of a sophisticated shade like fuchsia rather than pastel pink. I wind up buying pink items, because it is the most flattering choice offered, but then the item languishes in my closet, because I don't feel powerful in it at all. I feel childish or like an Easter egg or something. Perhaps I really need to get over that.