The primrose seed is a seed needed to clear the Henesys Party Quest.
The seed comes in 6 different colours.
Henesys Party Quest is an activity you can do together with the rest of a party in the MMORPG called 'Maple Story'.
Dude#1: "Which one do we need?"
Dude#2: "The yellow primrose seed."
Dude#3: "Done, I found it."