You can't do that easily. There are several alternatives at your disposal.
The simplest way is to create a Skin XML file of your own, in which you specify your own colors for your Application, you read it via a Class you create as well and you apply the new colors. This will keep things separated and ready for future changes. But note that you still won't be able to change how the Title Bar is rendered and other system-specific things, such as how the X and Maximize buttons look.
Expanding on point 1, you could create your forms as borderless and create your window with custom painting (override OnPaint) and images. This is harder to accomplish. You may want to inherit from the Form class and create your own CustomDrawnForm which you will use across your application.
Use one of the many control libraries out there, such as DevExpress. Some are free, some are expensive.
What you're trying to do is not very simple in Windows.Forms, and maybe you should look at WPF and other alternatives.
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