Had to think about it though, I usually work backwards, so-to-speak!
I usually have to start with a beer spec and then come up with the recipe!
Extracts are usually made to customer specs in large breweries, depending on how it's handled, whether it's dosed through machine, (runnier), or added manually to the copper, bloody tar.
Also as mentioned Ethanol (clear yellow) can be added to the beer before packaging if they realise that they are a little out of spec and because its not isomerised doesn't get too harsh and also really helps head retention.
CO2 extract is like dark green tar, but contains all if the hop soluble matter and can therefore only be used in the kettle, but has all hop essentials.
Iso, Tetra and indeed hop oils as you allude to, are very synthetic tasting. You can spot beers a mile off if used a little too much.
Regards
H