main.swift

enum Color {
  case Red, Green, Blue, Rgb(r: Int, g: Int, b: Int)
}

func to_hex(color: Color) -> String {
    switch color {
    case .Red:
        return "#FF0000"
    case .Green:
        return "#00FF00"
    case .Blue:
        return "#0000FF"
    case let .Rgb(r, g, b):
        return String(format:"#%02X%02X%02X", r, g, b)
    }    
}

var color = Color.Rgb(
    r: 255,
    g: 255,
    b: 255
)
print(to_hex(color: color))