Power of Love = Haki in its purest form.
It is the Haki that is truly capable of "transcending all" and the reason why Sanji can destroy lasers.
It is not a Colour, but a base element.
Yeah, I reached the same conclusion last month in who-knows what thread.
Basically, I see it like this:
Haki is your will, your want to impose yourself on others who stand in your way.
An uncontrolled burst of haki is just pure will, untrained, unfocused, unaimed.
CoA, CoO, and CoC are forms of your will that aren't instinctual but trained for a specific need: shield yourself, scan the environment, hurt others.
This is a haki that was molded by the user's intellect, so it's a few steps removed from its natural expression.
PoL, on the other hand, is a parallel form of natural haki in which your will is not that to impose yourself over others, but to protect others.
It's not an evolved form, like CoA, CoO, and CoC, but instead a natural instinct (thus stronger, because unfiltered by the mind), and directly aimed for protection of loved ones and nakama.
Take for example an ape.
It'll bash another ape's head in to become alpha male of their group.
And it'll attack other apes and predators to protect its child.
In both cases they're instinctual behaviors, but a momma ape trying to protect her little ones will always act more aggressively, and thus be more successful, than the one cocky ape who just wants to be boss.
Taking this ape analogy to its extreme, it's when the ape starts using a rock or a stick to attack or when it awaits for hours in the bushes to ambush its rivals that we go from natural haki to CoA/CoO/CoC.