code: func (a *Writer) Color256(f, b int) (int, error) {
  	size, err := a.WriteString(FColor256(f))
  	if size == 0 || err != nil {
  		return size, err
  	}
  
  	return a.WriteString(BColor256(b))
  }
docs: // Color256 输出 256 色的颜色信息