Like Dislike Puzzle - Hint

#189

One of my friend has a unique kind of choice. 
He likes Blue but does not like Indigo;
He likes Spinach but does not like Onions; 
He likes Avocado but does not like Persimmon;
He likes Shapes but does not like Forms;
He likes to work as Freelancer but not as an Intern. 
Actually, his like or dislike depends on some rules..
Can you guess, does he like Tomatoes or Corn???
And His Rule of like/dislike ?? 

  Difficulty Level - 4/5

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   Word Observation.