The Phaeton, Relief, probably a couple of others. Unfortunately, Brian Anderson's (he's one of the moderators here) www.esterbrook.net doesn't address this directly.
If it's a J, LJ, SJ, CH or H or other pen which takes Re-New points then a gold nib isn't from Esterbrook AIUI, except that the ``Sunburst'' 3xxx designs were available in gold-plated 8xxx versions --- more information here:
http://www.richardspens.com/?page=ref_info/estynibs.htm --- which sounds like what you have, which is a wonderfully nice thing to have! Congratulations!
(And the 3xxx non-sunburst nibs made in Britain were gold-toned as well)
However, one often finds Esterbrooks w/ Osmiroid nibs which fit and most of those are gold-toned.
Also, Fred Krinkle of the Fountain Pen Hospital in Los Angeles fitted gold Pentalic nibs into collars which could then be used in Esterbrooks. I've seen two of these come up on EBay and both were in pastel-coloured CH pens, so this might be what you have if it's not a sunburst nib. (Which is still really nice.)
And of course there's always the case of a Frankenpen.
William