David Tennant's famous quote is: "The sky is a burnt orange, with the Citadel enclosed in a mighty glass dome, shining under the twin suns. Beyond that, the mountains go on forever... slopes of deep red grass, capped with snow..."
So I found pictures. I thought that even if we can't know exactly what it looks like, a combination of them all might give us a sense.
This one is just beautiful. I think this is the kind of image 10 had in his mind at the time of his quote.
This is pretty, with the snow, and the two suns. No red grass though.
Evil Time Lord overlooks his barren planet that is stricken by war.
All of this images have an orange sky; but how do you make it look like it's not on fire?
It's interesting how the Doctor focuses on the citadel, and makes it seem so big, but compared to a planet, any citadel would be quite small. This picture makes it seem tiny... but giant at the same time.
It also looks like it's all about to go up in flames.
This is pretty, but somehow I can't imagine 10 and Rose going back and skipping through the fields of a planet that went up in flames and caused the Doctor so much distress.
This one is an interesting depiction, much more devoid of detail and more concept based.
Also, the sky is orange, but obviously not on fire.
I like this one because it clearly depicts the two suns.
Also, this version of the planet has water.