The 'gold' aventurine as far as I know is made using copper however it's not reddish brown, at least not in the pieces I have with aventurine in them.
extremely badly, but in real life the aventurine in the pieces of glass I have are bright shiny sparkly gold.
However, from reading that article, it does seem that once the aventurine is made, some parts of the final lump can be better than others (it says in the wikipedia article the heart of the mass can be the best bit). Therefore if the worst bits of the mass are used then perhaps it's cheaper and not quite as beautiful(dull browny in colour)?
Also if aventurine is then used in glass, then as I understand it, if it is not used at the correct temperatures, it can appear dull and darker (burnt? lol) in the finished article. I see this in some earlier Chinese glass (Dalian examples that were confused for V Nason Avventurine pieces) that used a lot of aventurine - it appears brown rather than gold in the finished piece where the Nason Avventurine pieces are utterly superb in their 'sparkliness'.
I have spent weeks trying to get my camera to work efficiently to photograph an Italian 19th century paperweight I have with aventurine in, to try and show it off to it's true effect.
This is the best one I can get (attached). In real life it's effect on the eye is superb, really
, it's a mass of sparkly shiny lights.