Must try a Mordant.

As a famous, suspected, pervert used to say:-
"Can you tell what it is yet?"
Dyed a few eggs this year, having missed last time. Onion skins are always a favourite and tend to leave rather nice patterns the way we do them. I tend to include a few flowers from around the garden. This year we had a number of Pansies and I was gobsmacked to find a purple/maroon(ish) Pansy left a green colour on the shell.
This is the outline of a Primula wanda: which, you probably know, is purplish/maroonish colour.
Hence the need for a mordant, preferable one which won't poison the eggs.

"Mordant
noun
1. A substance, typically an inorganic oxide, that combines with a dye or stain and thereby fixes it in a material."