As usual, you will have to zone after completing the previous Rhinostery quest.
Speak to Kerutoto who says that if you find a suspicious item, you should bring it to her.
If you are eligible for the quest Waking Dreams, you cannot begin Blue Ribbon Blues until you have accepted the challenge of Diabolos. Defeating Diabolos is not necessary to start this quest; however, you may need to talk to Kerutoto twice in order to do so.
If for some reason you'd like to keep the Purple Ribbon (for use on a job that can use it) be aware you normally lose it at the end of this quest. To keep it around, send it to yourself via the Delivery service as soon as you get it. Return to Roberta and talk with her again. She will ask if you've lost the ribbon, mention that it made its way back to her, and she'll give you another.
Check the Hume Bones after the NM has been defeated for a Blue Ribbon.
If for some reason you are unable to obtain the Blue Ribbon and zone, you will need to start the quest over. Talk to Kerutoto and Roberta will give you the Purple Ribbon back again. You will need to bring it to Kerutoto to examine, then zone and talk to her again to get it back in order to do the fight.
The purple ribbon you received from the goods shop in Windurst Woods seems to have a spooky curse on it. Kerutoto suggests that you search out the final resting place of its original owner in order to return it.