bgcolor="transparent" - valid or invalid? confused...

I'm looking at this page: 
http://www.jisc.ac.uk/index.cfm?name=event_hea_0605
and I'm seeing an interesting different in rendering between IE (6.0.2, 
xp, sp2, patched)& firefox (1.0.4)

Specifically, its the two tables in the body of the page.
In IE, the table has a fine grey border.
In Firefox, the boder has no boder, but has a blue background.

The only thing I have an concern with is the bit that says 
[bgcolor="transparent"]

The validator picks up on a number of errors, all of which I can 
understand, but passes this without comment

The W3 specs define bgcolor as taking an RGB colour code, or one of the 
named colour aliases, and "transparent" is not one of them.

Which is correct?

-- 
Ian @ home