Well, I give my ringneck doves green things for treats. I know they love celery, cucumbers, tomatoes, brocolli, etc. I think it's a good idea to give them things other than just seeds and grain. I've even given mine hard boiled egg before too.
I'm not sure how they would be with fruits like oranges and kiwi. I know that tropical birds love those kinds of things, but I haven't looked into feeding them to my doves.
It's very enjoyable to have a treat to give them, and some birds like certain things more than others. My one female dove loves peanuts.
How old are your doves, and do you have a pair?