"Keep our planet blue and green" is one of the Earth Day slogans I remember from the relevant events in which my scout troop participated when I was little. Celebratory banners presented an idealized picture of the globe in those colors, and participants in the event were given small evergreen trees in little pots to plant in the yard, for further promotion of greenness. I suppose blue and green were perfectly reasonable colors to be promoting for the environment in northern Virginia, where I grew up and lived until I was 18, and I really didn't think further into those color-based slogans when I actually paid attention to the holiday.
I didn't see a place to which those colors and the environmental generalizations associated with them really didn't apply until I moved to California in 2006. Sure, I'd seen pictures of deserts, but with those pictures also came the generalization that deserts are wide, flat except for sand dunes, uninhabited, uniformly brown, and full of enormous cacti. But seeing the desert in person - that was a whole different impression. I saw no cacti on my drive across the country, but there were strips and blocks of bare exposed mountains at nearly regular intervals, and I saw plenty of towns stuck in the middle of the sand, trying to be green and welcoming in an environment not so conducive to either.
And I think the colors of the desert are amazing. Brown is only a small part of the story. The palette of the exposed rocks can make the concept of a green swath of vegetation seem too monochromatic and boring. I'm currently taking a mapping class for which our field area is banded in greens, pinks, reds, yellows, creams, and even bright purples, all brightly contrasted against the blue of the sky. The generalized blue and green of streams and trees simply does not apply here, nor should it be made to apply. I have to wonder if the people living in those high desert towns get the same blue and green Earth Day slogans as the folks on the East Coast do, and whether it's deliberate or ignorant that they disregard the colors and characteristics of their local ecosystem in the process of constructing an unnatural environment by hijacking resources from their natural sources, far and wide.
But I digress. Plenty has been written about the development and deconstruction of the desert, far more knowledgeably and articulately than I could do. My point is partially that shooting for the blue and green of Earth Day posters is not the right idea for everywhere on the planet - but also that, while rivers and trees are indeed unique to Earth (as far as we know), the geology that lies underneath that layer - as may be exposed in the desert, for example - is just as unique to our planet and worthy of recognition and celebration on a day whose name suggests devotion to the entire planet.