func color() -> UIColor {
    switch self.highPower() {
    case let p where p <= 0.6 :
        return .gray
    case let p where p < 0.76:
        return .blue
    case let p where p < 0.90:
        return .green
    case let p where p < 1.05:
        return .yellow
    case let p where p < 1.19:
        return .orange
    default:
        return .red
    }
}