I've seen a few posts on the forum about the choice of Ubuntu to use a brown palette in the general theme of the gnome desktop. While I have no actual idea why this path was chosen, I suspect it may be due to a general trend in interface design that is moving away from the blue palette that Microsoft and Apple have been tweaking for almost twenty years now. Blue has been done to death -- and besides, it's a cold palette, and renders the desktop with a kind of formality and corporateness that's at odds with the personal nature of computing today.
Brown (and shades edging up toward amber) and green (olive green in particular), are currently the leading edge of visual design. These colors are organic, relaxed, and accessible. Perhaps you've noticed that the default icon themes in applications like Thunderbird and Firefox are generous with sandy colors and browns, and stingy with blue. You can see the cutting edge of this type of design on the site of Jon Hicks , who was involved in the development of the Firefox/Thunderbird themes. (You can check out his icon designs for Thunderbird/Firefox here.
Firefox and Thunderbird are two examples of leading edge design. Another example -- this time web design -- can be found at Dave Shea's, site (a palette of sand and red). Dave is the author of the new book "The Zen of CSS design."
Both on the web and in all kinds of leading edge applications, brown and green are the new blues. (I use a green and amber palette on my own site.)
Ubuntu is on the right track with their choice of palette. But a default palette is necessarily bland: it has to be simple and eye-candy-less, so that the average user is not going to be scared away. Hence the default chocolate wallpaper, and the Windows-like window controls (familiar to immigrants from the world of Microsoft, who comprise a large segment of new Ubuntu users). Many users will eventually be interested in tweaking their desktops, however. They will likely seek other, richer combinations of themes and hues.
Here are a few options:
Window Borders and Controls
(Change by selecting Desktop/Preferences/Theme/Theme Details/Window Border)
You know the function of the buttons at the top right of each window. You probably don't need each button to indicate its job. So why not use a more uniform set of window buttons that also matches the Ubuntu palette?
Install the H2Oridium theme from here. It's simply a matter of downloading the archive, browsing with the theme manager ("Install theme") and clicking on the file. You may or not have to close and then re-open the theme manager to see H2Oridium as a choice under "Window Border". It comes with several flavors, but the one relevant to Ubuntu is H2oridium-Amber, which will give you nice amber buttons.
The best icons for the Ubuntu palette (in my view) are the suede icons, which have been updated and adapted for Ubuntu by Nikola ("Ubuntu Guru"..). You can find them here.
If you're adventurous, the Buddha wallpaper posted by Jakeslife is great. It's available near the bottom on this page.
If you're not quite so adventurous, look at the aesthetic wallpaper set created by Jose Rangel. You can find quite a few of Jose's wallpapers here. The "Ubuntu dance" wallpapers are excellent.
For a visually exceptional GDM theme, check out fabiand's Tobacco Sky.
When you put all this together, you'll have a very organic and stylish desktop. Your friends on the Mac and in Windows fill feel envious (and maybe some of them will switch...)