Super Mario Bros. dev team explains why the clouds/grass are just palette-swapped

A portion of an Iwata Asks: Vol. 2 interview with Iwata-san, Tezuka-san and Nakago-san…

Iwata: I have the impression that throughout the entire series, the games have been put together with a very solid commitment to not “betraying the player’s expectations” or “spoiling their enjoyment”. But with the Famicom, you would have been working with a great deal of limitations. Did trial and error play a large part in the process?

Nakago: Yes, of course. For instance, we had to display all the graphics on screen using only 256 components.

Iwata: Yes, that’s right. Later on, a new integrated circuit would increase the number of available bytes, but at the time of Super Mario, the Famicom allowed a game cartridge to be able to contain just 256 components, each one of which consisted of 8 X 8 dots.

Nakago: Right. That’s why we strived to make the items take up as little space as we possibly could.

Iwata: And Tezuka-san would do things like put wings on the Koopa Troopas and suggest that you call them Koopa Paratroopas! (laughs)

Tezuka: (laughs)

Nakago: We’d use the same image for both clouds and grass, just changing the color.

Iwata: The clouds and grass look like separate objects, but actually they both use the same graphical elements.

Tezuka: Yes. It was fun back then when we’d have to come up with ideas like that.

Nakago: Even with mushrooms and flowers, we’d be looking to limit the bytes we used, so we’d draw half of the object then flip it around to display it.

Iwata: That’s why these objects are all symmetrical.

Nakago: That’s true of the stars too. They’re symmetrical. There was the advantage that you could get an object that was double the size using only half the bytes.