"Joyful" Funeral Attire?

I will be attending a memorial service for my fiance's mother, and his family has specified "joyful attire". I'm not sure what that means, but I'm wondering if a black dress, modest heels and basic diamond earrings would be appropriate. I also would prefer to wear a scarf to cover my neck (healing medialization laryngoplasty scar), and I have a light purple/pink flowery one that I would wear. Thoughts?