When using forms in a non-trivial way, it is important to share as much as possible to conserve resources. For this reason, color management should be separated from the toolkit when there are more than one form to handle.
Of course, it is possible to create one toolkit per form, but that is too wasteful if there are many forms. Instead:
Create one toolkit for all the forms that have the same life cycle. For example, if creating a multi-page editor, create one toolkit per editor and dispose it when editor is disposed. All the pages in the editor should share this toolkit.
Create one color manager (FormColors) per
plug-in. When creating the toolkit, pass the color manager to the toolkit.
The toolkit will know that the colors are shared and will not dispose them.
Use platform support for fonts and if possible, use
JFaceResources predefined fonts. Between default, 'banner' and
'header' fonts, you can accomplish a lot. Using many fonts is very confusing
for the user, and if you do manage your own, you must ensure alternatives
across platforms. The JFace fonts are guaranteed to work on all the
platforms Eclipse ships on.
Dispose the color manager on plug-in shutdown (don't assume that plug-in shutdown also means platform shutdown - Eclipse runtime can uninstall your plug-in dynamically while the platform is still running).
Use form color manager to allocate all the colors needed by the forms.