From TFA:
“Various combinations of the eight Landsat 7 spectral bands were selected to create the vivid RGB composites that we have featured.”

Long and short of it, they are composite images of different wavelengths, and they assign each a nifty color to come up with the exaggerated results. Same thing they do to Hubble pictures by assigning colors to different elements and wavelengths to make pretty space pictures, as opposed to if you looked at say, the Orion Nebula, through a telescope with your own eye it just appears a smudgy grayish-blue.

There is no photomanipulation done to these, although we used photoshop to put the bands together. All we did was put three of Landsat’s eight bands in a RGB combination, and then adjust the contrast. Most of them use infrared bands; some of them are true-color, using the bands that approximate human vision.

I created about 80% of the images in the original show, and about half of the ones in the linked article. I might not be remembered for anything, but I know these images will be.

So maybe red is 0.4 * infrared band 1 + 0.6 * infrared band 2, for example. They’d normally be picked to make it easy to see what the user is looking for, but it gives you some leeway for artistic interpretation of a scene sensed in a way that doesn’t directly match what a human would see.