I understand that but if they have never eaten beige food then they don't know to gravitate to it. That is often also a weaning issue.
One of my DC has ARFID and the bulk of his diet is beige food because its that or starve, and contrary to popular opinion there are children who will let themselves starve if there are no acceptable foods.
He had zero interest in weaning, food upset him from the get go and he would not tolerate it. By 18mo he was pretty much living on Ready Brek and bananas and we were offering him an ever expanding list of refused foods. You can bet your arse I eventually offered him beige food because I was offering him anything and everything trying to find things he would eat.
Now he will eat chicken dippers (must be Birds Eye, they're softer and less fibrous than other brands), cucumber (circles only), plain baked potato (no butter, no filling, not mashed/fluffed up, just cut open and served), plain pasta (white pasta, fusilli only, no sauce), Nutella sandwiches (one slice of white bread folded over to make a sandwich, no butter), Weetabix (two, stacked in the bowl not side by side, milk up to top of the bottom biscuit, no honey or other flavourings, must be Weetabix brand as own brands tend to be square corners not rounded and so are "wrong"), bananas (the small kids variety, must have no brown spots, all peel and string removed), plain chicken breast (no seasoning and the outside part peeled off as its 'crusty'). He will very occasionally eat sweetcorn, "pizza" (the mega cheap ones with a very slight brush of sauce and a few strands of cheese), and sausages (Richmond skinless only, cannot be too brown or he'll consider them "burnt", served sliced). He has a glass of milk every day and a good multivitamin.
When you have a child who is that rigid about food, you feed them what they'll eat and if that happens to be nuggets and waffles then it'll be nuggets and waffles (DS won't eat waffles, too many holes).
For the record, he dances along the line between healthy weight and underweight. When he's going through an anxious or unsettled period he gets even more controlling and dips below it. When they had the healthy eating talk at school and he was paranoid he'd get fat, he dipped below it. When he's ill, he dips below it.
My other disabled child wouldn't touch nuggets with a bean pole but would probably eat the bean pole. He has PICA and he doesn't know when he's full, he also gets sensory comfort from chewing/swallowing. He will literally eat until he vomits. He tends towards healthier foods however, unsupervised, would eat them in huge amounts.