Eggs! Boiled! In tea! With salt! And spices! Pretty simple. The details of course vary. The traditional way is a hard boil from a very long simmer; modern cooling technology offers the possibility of a soft boil followed by a long marinade in the fridge. The type of tea used, spice mix, and other additions will shift the result around.
Be sure to break up the shell really well, otherwise the marinade will not really get into the egg. How concentrated the marinade is may also be important. Smaller eggs should present more surface for the marinade than a jumbo will?
Apparently old eggs stick to the shell less on peeling. Or you can add a bit of baking soda to the water, but that might affect the flavor.