实体的CAD颜色索引值

enum Color {
  kByblock = 0,
  kRed = 1,
  kYellow = 2,
  kGreen = 3,
  kCyan = 4,
  kBlue = 5,
  kMagenta = 6,
  kWhite = 7,
  kBylayer = 256
};