colorm.go
func (c *ColorM) Concat(other ColorM) {
	c.impl = c.impl.Concat(other.impl)
}
func (c *ColorM) Concat(other ColorM) {
	c.impl = c.impl.Concat(other.impl)
}
// Concat multiplies a color matrix with the other color matrix.
// This is same as muptiplying the matrix other and the matrix c in this order.