func hexModel(c color.Color) color.Color {
	if _, ok := c.(Hex); ok {
		return c
	}
	r, g, b, _ := c.RGBA()
	return RGBToHex(uint8(r>>8), uint8(g>>8), uint8(b>>8))
}
hexModel converts a Color to Hex.
package color
import (
	"fmt"
	"image/color"
	"strconv"
)
var HexModel = color.ModelFunc(hexModel)
type Hex string
func (c Hex) RGBA() (uint32, uint32, uint32, uint32) {
	r, g, b := HexToRGB(c)
	return uint32(r) * 0x101, uint32(g) * 0x101, uint32(b) * 0x101, 0xffff
}