The Aruch HaShulchan in OC 494:5 seen here mentions a minhag to put saffron in the food on Shavuos due to the fact that has a pleasant smell which alludes to the passuk in Shir HaShirim לריח שמניך טובים.
וגם נוהגין ליתן כרכום שקורין זאפרע"ן בהמאכלים והתבשילין, מפני שמשמח שיש בו ריח טוב, על שם "לריח שמניך טובים"
[Printed immediately afterwards is the parenthetical statement: (עיין מגן אברהם סעיף קטן ו בשם הזוהר, וזהו כמו שכתבתי). but that Magen Avraham has nothing to do with the saffron statement and is only talking about to the idea right beforehand about how eating dairy hints to strict law changing to kindness]
I would like to understand more about this saffron minhag. Where did he get this from? Who actually did or does this? Why specifically saffron, don't other spices have nice smells as well?