You can use style effects, such as typefaces, to highlight differences in information as well as using colour. You can also add text labels to a graphic link or a button.
For example, don't say "Please select an item from those listed in green." Instead, make sure that information is available through, for example, a font effect.
To test whether your document still works without colours, look at it with a monochrome monitor, with your browser colours turned off or print it on a black and white printer. See how your page looks and this should tell you if you need to add cues.