Cories go a cream colour, (maybe a hint of yellow in some breeds I don't know) if they're fertilised and should get noticable black dots where eyes are inside the eggs as they develop. Best bet is to get a very finely meshed breeders net and place the eggs in there. Get a good flow of water into the net, maybe place it near the filter outlet?
If eggs are stuck to side of tanks then use a razor blade or a credit card thin object and slide them off, that way they don't get damaged but over handling.
Depending on the breed cory eggs hatch after about 4-5 days but could be longer so be patient!
Darn, just seen that Diddlebug answered already! Sorry!!