You people just remember that any complex design slows down the forum very much, and people don't like it too colorful, it confuses the eyes. All the great websites around the world are always simple but designed great. Background as whole image never works well on all computers. Some view it from Laptops, some from Netbooks, some from Tablets and some even from Smartphones so, to fit all the needs, the background needs to be something like now. Also note that 0,59 KB for a background is great and using a whole image would mean more than 100 KB for sure but it will be much more than that.
Grey is the ultimate color of the web. Its the fact. If you change something change it but without gray, its all nothing in the end. We tried many times with completely other themes and members disliked it in general every time. Then we end up at grey+color.
What I want to say is that many people like the look as it is, or they will like it better when they see how awful new one is, which happened in the past many times. So if new skin is about to come it needs to pwn everything else it will end up as wasted time
Im not forcing anything instead I just reminded of facts from past.