fantasy book: theobroma

I read the word theobroma somewhere some time ago and it reminded me of a book I must have read, but I can hardly remember anything about it. Only that it had this stuff in it, theobroma, I believe it was multi-coloured? And it did something, something magical, but I don't remember what. I vaguely seem to remember that you shouldn't eat too much of it, but I'm not sure about that.
If I read this in a book, it must have been a long time ago, or I'm sure I would remember more. Does this ring a bell for anyone?

Quite possibly Kage Baker's Company series. (Start with In the Garden of Iden.) Theobroma seeds are used to make chocolate, and the immortals in her series use chocolate...which they just call theobroma...as a sort of mildly intoxicating drug...it has a different effect on their nervous systems than on those of regular humans.

Are you thinking of Kage Baker's Company books (they start with In the Garden of Iden)? Theobromos is another name for chocolate, which has a narcotic effect on the immortals therein.

Great minds think alike :-)

It's the first thing I thought of too, until the part where the OP says it was a "long time ago" - the Company books are relatively recent.

Theobroma is a feature in Poison Study by Maria V Snyder - it makes the consumer more open to magic. Probably too recent to be the one you're looking for though.

#5--the first Company book was published in 1997, which while not a LONG long time ago is long enough ago that many details could have faded...

*blushes*
I suppose it wasn't as long ago as I thought... I'm pretty sure it was Poison study. I was convinced the book couldn't be in my bookcase, since I remembered so few details, but I guess my memory wasn't functioning the way it should. Because the book is in my bookcase and I've even reread it 2 or 3 times...
Thanks for your help!