Hi, Peter:

While I like the idea of color coding, not that you asked < s>, but "red" usually means "danger" or "warning" to users. IOW, frightens them. Just my .02 U.S.

One could always simply add "(required)" to the label if possible with the screen real-estate. Simple/unambigous and more easily localized, I'd imagine.

>The way that I have signified mandatory fields in my applications is to make the colour of the label red.