It might be a phase. I have two kids ages 3 and 5 that eat really well and will try anything, however, they can love salmon one day and not want to touch it the next. With your son, keep doing what you are. Offer but don't force. Offer a variety of veggies, plate them in different ways. With mine, a fun thing we did at that age was take a muffin tin with 6 slots and put different things in each slot - don't fill them up, just a bite or two in each. Set it down and let him graze. Peas, sweet bell pepper, carrots (nuke them for a bit to make the a little softer - if needed) or you could do shredded carrots, crackers, cheese, anything bite size. My son gets hooked on mac and cheese and my daughter pb&j, since I know they love these foods, I make them as healthy as possible and offer other foods I want them to try first. Again, I never force, at the most, I might say, "just take one bite, if you don't like it you don't ever have to eat it again" I'll usually keep trying with that food every now and then till I'm sure it is something they just don't like. Also, another thing I do if it is something I just want them to eat and I know they like it, I might say, "OK, just 3 bites because you're 3 years old" 5 bites for my daughter because she is 5. They have fun doing this. You could say to your son, just one bite since you are one. One more thing that works although it is a little sneaky on our parts, just make a plate for yourself (make it for him but pretend it is for you) then go and sit down with it. He'll be curious, you can say, sorry bud, this is Mommy's plate, if he looks like he wants something from it then say, OK, I'll share it with you this one time... (-: I don't advocate manipulation but this has worked for me in the past and it was a win win.. they feel like THEY made the decision - you didn't demand anything.
Sorry for being so long winded on my answer - I've had way too much coffee!!
M.