Has your therapists mentioned him wearing a pair of lens colored sunglasses when he eats. I know it sounds far-fetched but this would "change" the color of the food and it might get him to eat. Make like u are having a party..on a beach party, etc and give him foods he likes first and then add a few new ones..maybe same texture. Don't give up after one try..keep re-introducing the foods and don't let him drink alot of fluids before he eats..this will fill him up. A nutritionists maybe able to give you some help. Happy eating!! Good luck!
Sometimes occupational therapy can be of assistance with problems related to the texture of foods and children's reluctance to eat a range of foods. Generally, though, such preferences do not result in health problems for children, and this is the key. Be sure to be checking with your pediatrician about your son's overall development. Also, sometimes incentive systems (quid-pro-quo) can be straightforward and useful, particularly when it comes to inducing children to take medications.