Most of the people think that these desktops can only be created in 3D rendering applications such as 3D-Studio or Cinema 4D. Well I will show you how to create such a desktop using Adobe Illustrator's gradient mesh tool.
In a first step we draw a rectangle in the intended size - probably about 2560x1600px so that it can also be used on Apple's 30" Cinema Display. Use Illustrator's "Transform" panel in order to control the exact size of the rectangle.
Afterwards we fill the rectangle with the intended color. In this case I've chosen a generic blue, as it is used in the Blue Crystal collection. In a next step we select the rectangle, select the gradient mesh tool from the tool panel on the left and add a single point (anchor) by clicking the left mouse button.
In a next step we create two further anchors and assign them slightly different colors using the eyedropper tool.
Now we can select all three anchors via the lasso tool and move the selection in the intended direction.
Now that we have created the basic shape we can either optimize it or add additional forms until we get the intended result.
In order to get the 3D style we have to select the bottom anchor via the direct selection tool (1) and drag its bottom handle (2) to the top.
The result should look similar to the screen below. At this point we have finished the work in Illustrator - let's move on to Photoshop…
Now we can copy the artwork to Photoshop. Duplicate the layer and set the blending mode of the new layer to "Overlay". Now select the "High Pass" filter from the "Filter" menu, choose a radius of about 10px and confirm. After the filter has been applied you may set the layer's opacity to about 70% if the High PAss effect should be to intense.
If you are using a TFT display you may recognize that the gradients of our desktop are not that smooth. The reason for this effect is that TFT's normally can display less colors than CRT monitors. In order to optimize our desktop for TFT we have to add some grain.
In order to achieve this effect we create an additional layer, fill it with black color using the paint bucket tool and apply the grain filter, that can be found under "Filter/Texture/Grain". Afterwards we desaturate the layer (Image/Adjustment/Desaturate), set its blending mode to "Overlay" and once again reduce its opacity to about 5 or 10%. You will recognize that the gradients are now much smoother.
Click to enlarge