Marking eggs and chicks

I just use a pencil.  It won't leach through the shell.

For marking chicks, I think people use coloured cable ties or freezer bag twists (apparantly you can get them in colours on ebay) until they are big enough for  leg rings.

You have to be careful though and check to make sure thy aren't too small very frequently (which is why the tie twists are probably a better option).

LOL!  OK, I'm a bit younger than you

I guess a water based marker, rather than an alcohol based one then!

Freezer ties might still be the way to go for marking though - easier to get off than cable ties... but still fiddly when you are dealing with a wriggling chick 

Try wing tags, they're on for life.

Chicks can be wing tagged at a day old. Some can be done by hand others use an implement similar to pliers.

I don't see why you can't use food dyes. You may have to top it up as I don't know whether or not it would wear off, just until they are large enough for leg rings. Ijust wonder if the freezer/cable ties might be a bit 'sharp'!