Update: For Easter Day, I boiled up yellow onion skins the day before and left them to sit overnight, then boiled our breakfast eggs in them this morning, with this result:
In German supermarkets, they sell boxes of six or ten hard-boiled eggs, dyed pretty colours, all year round, and I often buy them, both for us to eat at lunchtime and to take home for my mother, who likes them.
However, we are not in Germany, and won't be going for another month, and it is Eastertide. I have vague memories of reading that one could dye eggs with natural ingredients, and then a picture form this post popped up in my Facebook feed. So I had a couple of experiments.
WARNING: The eggs, while perfectly edible, are horrendously hard - I still haven't quite perfected them. The ones you buy in Germany are hard-boiled, of course, but not to the extent that they get a black ring round the yolk, But I think it's probably difficult not to when making them at home.
The basic recipe is very simple. In a stainless-steel saucepan you put your dyestuff of choice (I used firstly 1/2 packet of frozen blueberries, and then secondly the skins of 5 or 6 red onions), and a large spoonful of vinegar. Fill the saucepan with water, bring to the boil, and simmer for 20-30 minutes (don't let the saucepan boil dry, which I nearly did!). If necessary, top up with cold water and bring to the boil again. Let it cool, strain out all the solids, and then add your eggs - as many as you can spare, or as can comfortably fill the saucepan, bring back to the boil and simmer for about 10 minutes, then let them cool in the liquid. If they aren't coloured enough, let them soak a little longer. Remove from the water and admire! When cold, polish with olive oil.
This was my first attempt, with blueberries: 
and the next day's, with red onion skins:
Of course, the colours will vary according to whether you use white eggs (not so easy to get here, but Lidl does sometimes have them) or brown. I think for Easter Day I'll use yellow onion skins (maybe make the dye bath the night before) and then just boil the eggs as normal for Easter morning breakfast. We shall see....
