colorm.go
func (c *ColorM) Add(other ColorM) {
	c.impl = c.impl.Add(other.impl)
}
func (c *ColorM) Add(other ColorM) {
	c.impl = c.impl.Add(other.impl)
}
// Add is deprecated as of 1.5.0-alpha.
// Note that this doesn't make sense as an operation for affine matrices.