Apple has its own Java 1.3.1 API link posted, and there is in fact no
field in the Color class named BLUE.  The same was true of those from
Sun.  But with the 1.4.1 and 1.4.2 APIs, Apple no longer even has any
API JavaDocs posted (that I'm aware of).  Instead, they only offer an
API for Apple's extensions.  In either case, their standard APIs matched
Sun's.

So the question to answer, if indeed the error is related to Color.BLUE,
is just which Java is in use on the machine where this error occurred.  
Java 1.4.2 is not available in OS X 10.2 and earlier, if I understand
correctly.  And it wasn't available when 10.3 was released, so it won't
be there on 10.3.x systems unless an update was applied.  And even then,
only Safari would use it automatically -- most other browsers will need
some kind of help, if they can use the newer Java at all.  I'm pretty
sure that's true of Firefox too, which I use, but I can't say positively
(not having looked into the issue, as I don't use many pages that have
applets on them).

You may want to prod the Mac user in question for more certainty in
what's present and the conditions under which the error surfaced.

= Steve =