colorm.go
func (c *ColorM) Apply(clr color.Color) color.Color {
	return c.impl.Apply(clr)
}
func (c *ColorM) Apply(clr color.Color) color.Color {
	return c.impl.Apply(clr)
}
// Apply pre-multiplies a vector (r, g, b, a, 1) by the matrix
// where r, g, b, and a are clr's values in straight-alpha format.
// In other words, Apply calculates ColorM * (r, g, b, a, 1)^T.