Babies tend to do that sometimes. So long as he is getting other food and fluids, it is fine.
You could use meat and vege combo when cooking porridge - fish, beef, etc with pumpkin, beetroot, asparagus, broccoli, cauliflower, etc etc all those superfoods!
Don't forget avocado, too! You might also want to try putting some milk powder into cereal.
Again, just make sure he has enough fluids and food.