Rose Lalonde’s Land of Light and Rain is characterised in part by its shimmering rainbow water. Why does it look like that? Perhaps it’s because it’s covered in a thin layer of oil?
Let’s look at this sequence. Rose Lalonde stabs an ogre in the eyes and rides its corpse down a LOLAR waterfall.

As pointed out in Andrew’s commentary:
…this attack presages the moment when Rose does the exact same thing to Guy Fieri as a fifty-something-year-old in an alternate universe.
Which we can see here:

Notice that this is a waterfall of the blood of all of Guy Fieri’s victims.
You’ll also notice that in the first few panels of the former sequence, the ogre bleeds some kind of black substance out of its eyes, as opposed to blood. I’m inclined to think that, since the first incipisphere underlings we see are oil imps who leave trails of black liquid after them everywhere they go, this liquid coming out of the ogre’s eyes is also oil. It’s worth noting also that this is a lime ogre, and that in real life limestone is heavily associated with hydrocarbons like oil, often containing pockets of it inside.
So in these two parallel instances, we have an ogre bleeding oil from its eyes and a man bleeding blood from his eyes, both falling down a waterfall. In the latter instance, the waterfall is stained with blood; so in keeping with this parallel, it follows that the former waterfall would be stained with oil, right?
Oil, of course, is primarily associated with John’s Land of Wind and Shade, but John and Rose’s worlds have always been connected by similar (Wind and Rain) and opposite themes (Shade and Light). The waters of LOLAR were intended to be polluted from a very early stage, in fact, albeit by a different chemical, if Andrew’s Book 2 commentary is anything to go by:
I also had the idea that these 4 substances [oil, chalk, amber and uranium] would serve as various contaminants on their planets, in ways relevant to their personal quests. John’s planet and all its pipes were clogged with oil, Rose’s ocean planet poisoned in some way by excessive chalk, which the islands were made of. Dave’s planet was covered in gears, which would be gummed up by sticky amber sap. And Jade’s was going to be in some way affected by fallout (nuclear winter?).
But what could it possibly mean? It’s hard to say. The topic of liquids with a colourful oily film on the surface has been touched upon once before in the comic. Rainbows - the result of mixing Light and Rain - are associated with the Time aspect, as is oil itself.
A symbol of Lord English’s malevolent omnipresence? It’s been suggested that oil is representative of English’s corruption, since it was the same technique that John used to get rid of both LOWAS’ oil and Caliborn’s Special Stardust glitches.
A symbol of obscured information? Crystal waters of the sort found on both Rose’s planet and her fellow Light player Vriska’s are a symbol of knowledge and divination, and being a Light player seems to involve “seeing through” things that obscure the truth, like the opaque surface of a magic cueball. With oil covering all of LOLAR’s oceans, the whole planet becomes a magic cueball - note that this interpretation works whether LOLAR is polluted by oil or chalk, and that chalk is applied to a cuestick before a game of pool.