Summary: You can make surprisingly rich multi-color gradients with Visio 2007 and some code.
The Visio 2007 User Interface Allows multi-color gradient fills (i.e. 2 gradient stops, one at the start and one at the end), but only supports a single transparency for both stops. If we had the ability to specify different transparencies for the stops, we'd be able to create some nice effects.
Here's what we can create:
Visio's graphics engine supports this feature, it's just not exposed in the User Interface.
Using this technique we can combine multiple shapes with different colors and transparencies into a single beautiful gradient.
To get the image above, just draw 5 different shapes and then stacks them on top of each other:
The code to generate these can be found in the VisioAutoExt project on codeplex.
If you get creative with the gradients you can create an image like this.