Return a color based on percentage. 0% is Red and 100% is Green

FixedColors.swift

static func colorForPercent(_ percentage: Double) -> UIColor {
  switch percentage {
  case 0..<0.33:
    return UIColor(hex: 0xE02020)
  case 0.33..<0.66:
    return UIColor(hex: 0xFA6400)
  case 0.66..<1:
    return UIColor(hex: 0xF7B500)
  case 1:
    return UIColor(hex: 0x6DD400)
  default:
    fatalError("Bad Input: percentage must satisfy 0 <= percentage <= 1")
  }
}