Around 1980 I used to get a citrus drink that was very bitter tasting but had an aftertaste that grew on me. I think the product was bottled in Spain and was made from an unusual citrus fruit (possibly citron but I am not sure). The dark green glass bottle it came in was small, maybe 6 or 8 ounce size. I don't remember the name but does this ring a bell with anyone? thanks.
Sounds like it could be Bitter Lemon. Both Schweppes and Canada Dry make it, as well as a number of smaller manufacturers (Riggs & Forsyth I've tried, seen a couple of others). I have seen and purchased Bitter Lemon (I think the Canada Dry) in small green bottles.