i work with the .net framework, all day, and when using predefined colors, it can be a little bit confusing and a lot irritating. however, i have recently found a chart that makes things a whole lot more simple.
C# Developer Resources has a a great chart that is auto generated from the Named colors in System.Drawing.Color here is a link and a preview:
i have also found another more Clinical Table of the named Colors. here is the Link and the preview.
i have found these two to be very useful when trying to mock-up a screen, or site.
for those of you who may not be working with .Net, but want a simple way to set color schemes, i recommend Kuler by Adobe. it helps you select color schemes based on many of the common design practices( analogous, complimentry, Triad, etc...) and you can even share them.
one of the nicest features is the plugin for the CS2( and Above) adobe products, that allows you to use this tool inside popular adobe products.