I would put that in the category of sensory disorder. Lots of people are picky though because they don't prefer something. I've been able to get preschoolers to try things just because they know it's a safe place that they wouldn't touch at home because their parents were fine with them not eating it! At school we'd talk about the plant it came from, show pictures, talk about the taste and texture, make graphs about it etc.
Life is hard and while I never advocate or bribing, punishing or cajoling during meal time I do believe that making it fun can make all the difference for some kids. And, while we're on the topic, adults too! I like pretty, fun food better than boring, plain food!