When my project grows too big, it also get harder to recognize the growing number of classes. I'm looking for a plugin for eclipse, that makes it easier to differentiate the classes by assigning icons or colors to them.
Alternatively I'm looking for any tools, plugins or advice to see through the jumble of classes.
(Currently I'm only using packages for grouping classes)
You should be using packages to the full extent. That means, whenever you find that at least 2 classes in an already existing package share a common aspect, think about moving them into yet another sub package.
Over time, this can lead to quite long package names like org.eclipse.product.addon.technology.ui.someview.listeners
. As those are not easy to browse, use the compressed package name display of Eclipse, which allows you to replace any package path by an arbitrary string (only for display in the package explorer). So your very long package names get shortened like here: