One thing to note at the beginning, the aliens in the original were very liberal. They don't care what any species does on its own planet as long as no one tries to initiate violence between planets. They set up, in Klaatu's words, a police force of robots to kill anyone who tried to initiate violence, and that was the entire scope of the galactic government. The government doesn't care what you do as long as you don't try to hurt anyone else (you can hurt yourself all you want). The supreme directive of the aliens is that interpersonal violence is the supreme evil. And all involvement in the galactic government was voluntary. You didn't have to abide by the interplanetary law if you wanted to keep to yourself on your own planet, but if you did decide to join the galactic government there was no way to go back on that decision.
The aliens in the remake are authoritarian, if not outright genocidal. They glorify violence if it achieves their goal of protecting barely sentient life like bacteria or moss. Interplanetary law is imposed on all planets without any warning or announcement. Not only can you never leave, you don't even get to decide whether you join or not, you are born into the legal system and there are no alternative systems to escape to. The galaxy is a prison and you're stuck in it.
Now to think about colonialism you have to think about how the message from the aliens in the remake does not make any sense.
Planets that can support complex life are so rare in the universe that the aliens have to kill all humans because humans are polluting the Earth. And to do this the aliens don't use some hi-tech weapon that will kill ONLY humans and spare everything else, they release an exponentially expanding plague of robots that eats absolutely everything, including rock, erasing completely a biosphere that took millions of years to develop, and then they will re-seed the now totally barren, lifeless Earth with animals they saved from their zoo. And they think this plan can actually work. You strip the planet down to bedrock, cover that with a blanket of gazillions of dead robot bugs, and then place a small handful of plants and animals rescued from the handful of ships, and hope that the one pair of elephants doesn't eat the one grove of trees that gets planted and dooms all life on Earth to extinction permanently because now not only has the biosphere been wiped clean but all the zoo animals have died.
This plan can never work. Raising endangered animals in captivity and releasing them into the wild only works because there is a wild to release them into. If the wild is destroyed completely and the endangered animals are released into barren rock then the released animals will die too because there's not enough food to go around.
What if the aliens terraform the Earth again over millions of years? Maybe they will, but that still sets life back millions of years. They still have to keep the elephants alive on the tiny little ships for millions of years, and they clearly didn't bring enough plants with them to do that, unless the aliens feed all the animals the magic placenta material until new forests have developed. You can't have terraforming and Noah's Ark at the same time. If the aliens want to terraform the barren Earth then they'll have to accept that all the complex life they claim to cherish so much will go extinct, by their own hand, and evolution will have to start over again from bacteria. If the aliens want to preserve complex life they would have developed a human-specific virus that would have spared all other species. The aliens want to do both at the same time and would probably end up achieving neither.
So, since the alleged motivation and plan of the aliens makes absolutely no sense then we can suppose one of two things: 1. The writers never bothered to think things through and just got drunk and slapped a CGI-crapfest together in a weekend, or 2. The aliens are lying.
We're rational beings here, we know 1 is the correct answer, but just for fun let us assume the writers were intelligent and what they really intended was 2.
The aliens were hostile from the beginning because they wanted the Earth for their own use. They come to Earth and tell a couple of humans "You are not using your resources efficiently enough. We can use them more efficiently, so you must die." Mind you the aliens can control all electricity and all electronic devices, they have an unlimited power source, are capable of faster than light travel, and they can cancel inertia, they could easily transmit a signal to TVs, radios, and computers simultaneously without needing to physically meet at the UN building. This fact alone makes it look like a setup. The aliens could warn the planet but they decide to warn a handful of military personnel instead?
The aliens are classic invaders, and they are justifying their invasion in colonialist terms. The Chinese are not "invading" Tibet, they are "peacefully liberating" it, because the Tibetan people do not know how to live properly and must be "educated" and freed from the "oppression" of their government. Meanwhile half the population is "liberated" from living, all the Tibetan resources are extracted for Chinese use, and all the Chinese nuclear waste is dumped in Tibet.
Similarly, the aliens are not "invading" the Earth because they want to exploit it for themselves, they are "peacefully liberating" the Earth from the human "infestation".
Think about it. What is the difference between what humans are doing and what all other species do? Contrary to what Agent Smith said in the first Matrix, animals do not seek equilibrium, equilibrium just establishes itself naturally because the exploitative capacity of any group of animals is finite and is usually in line with the capacity of other competing species to avoid exploitation. When all the restraints are removed any species will use up all available resources until nothing is left. This is seen in every situation with an invasive species. Rats accidentally land on an island and within a few years all the native ground-nesting birds are extinct. The rats were not seeking equilibrium, they were following their biological directive to seek out resources and use them to make more rats. At the very least one can say humans are no more selfish than any other species, just that human capacity far exceeds that of all other species, so there is no competition, humans completely dominate in every environment, in every sphere of activity. In that sense humans are the most animal-like animals on the planet.
The one thing Humans have beyond other animals is rational intelligence. As smart as they are, chimpanzees and dolphins not only don't care about the environment, they do not know what an environment is. Not too long ago, in the grand scheme of things, humans developed the concept of an environment and realised "If we follow our biological directive and eat everything then there won't be anything to eat in the future, so if we want to survive we have to put limits on our biological directive and utilise the available resources in a more efficient way." Humans are the only creature on Earth that has ever had that thought. Humans are then, simultaneously, the only creatures capable of destroying the biosphere, the only species capable of preserving the biosphere, and the only species that knows what a biosphere is.
And in 4 billion years that thought has only arisen ONCE. The very same thought the aliens claim to profess only ever arose in ONE species on the Earth, and the aliens want to exterminate the ONE species like themselves, the ONE species that had moved beyond instinctual selfishness to rational selfishness and, in some cases, rational altruism. (It is mysterious to note that the event that led Keanu to spare humans was a single instance of a mother comforting her child, which is something most mammals do to preserve their own genes and is thus an instinctually selfish act, rather than, say, agriculture, or treaties limiting fishing or pollution, or the whole concept of protecting endangered species, or nuclear nonproliferation treaties that have done more to protect the environment than anything.)
The aliens, then, are more selfish than the humans. The aliens are not more moral, they just create moral-sounding language to justify their selfishness. This is the same thing all colonial powers do. The natives are too ignorant, or to racially inferior, or they are simply being oppressed, and so the moral colonialists must move in and take over, kill the ruling class (the humans) and use their technological, intellectual, and moral superiority to uplift the lives of the oppressed natives (other animals and plants). Not enough is known about the aliens' culture to say for certain which mode of colonialism best applies, but they seem very similar to Communist China to me.
Was that what the writers intended when they came up with this remake of the great sci-fi classic? Not a chance, they were just making a popcorn flick, but it certainly has been entertaining to over-analyse the film.