I used to be really bad - up to the age of about 16 
Beige foods, genuinely disliked veg (would make me 'feel' sick). Would eat fruit, but would rarely actually do so 
  
As I've got older though, I've grown out of it quite well. I'm still a bit of a fussy eater, but not anything like where I used to be. 
I put it down to a few things -  
1 - Having girlfriends. Feeling embarrassed going to a GF's house and not eating whats put in front of me. 
2 - Cooking myself. This has really helped out as I can push the envelope a bit at a time and experiment in different ways of cooking the same stuff. Its amazing what you'll find out you like when its not just basic steamed/boiled veg. 
3 - Getting fit. Going to the gym motivates you to eat and generally live healthier. I hated coming in from the gym and throwing in a pizza - it's counter productive. It feels really good to have a work out and then eat something healthy. 
  
As said though, these days i'm pretty good.  
Really like soup (home made), and it's a great way of getting veg in my diet without having to sit there and chow through a load. You can also add spices and herbs which completely mask some flavors. 
Green leafy salad along side stuff like fish is really easy to eat - and remember they are all quite different. Lettuce is boring. Rocket and watercress are really nice 
Also helps that this year I'll be moving in with the lady who's also pretty healthy and so we'll be eating together