eating green

Should I be worried that my child will not eat?  He basically only eats fruit now.  He would survive on milk alone if we let him, but we try really hard to give him food before we offer him milk.  It is hard though, when he's furiously signing milk and please and it's always a constant battle to get anything in his mouth. Or if you get it in his mouth it comes right back out. 

I know that he'll eat when he's hungry, but seriously? Can he just subsist on fruit and milk?  He used to eat yogurt and a few veggies willingly. He would always eat a chicken nugget.  Sometimes he'll eat a grilled cheese, but for the most part he rejects all food now unless it's fruit.  Tell me how I can not worry.

In Target the other day Josh was begging for something to eat and of course I had nothing in the diaper bag. I did have a bag of Goldfish in the cart that I was planning on buying and I never do this, but for some reason I opened it and handed him a few right there. Well, these were those colored Goldfish and he ate all of the ones I gave him and handed back the greens ones. Yes, apparently he can't even taste green Goldfish! Goldfish for Pete's sake!