couple of variations seen on Youtube, including boiling the egg wrapped in pantyhose, with a cilantro leaf against it to make a pattern on the shell. I also tried wax designs on the egg from a candle...didn't work, most of the wax came off in the water.
If you want to do it yourself, you'll need skins from onions (I had 5 or 6 reds, probably around 10 yellows, obviously the more the stronger the dye), vinegar and eggs. Boil the onionskins in enough water to cover them plus two tablespoons of vinegar for about 20 minutes. Strain the onionskins out and let the dye cool. Then boil the eggs in the dye. I boiled them as you normally would hard-boiled eggs (15 minutes). You can do them longer but eventually the eggs will become inedible. If you don't like the color after 15 minutes just let them cool in the water and the dyeing process will continue. You can even soak them overnight.
If you want designs, take a cilantro or other edible leaf and place it against the eggshell, then wrap in pantyhose and tie it with a twisty.
As for the bright red eggs Yia-Yia used to produce? Research suggests she may have used Rit fabric dye. Sometimes traditions are better left unrevived.