In my opinion, your high school sophomore should be allowed to wear whatever he wants to wear to school. Battles with teens about clothing and hairstyles are not productive and may cause unnecessarily, fractured relationships between parents and children. Your husband should remember how important it was to fit in when he was your son's age. Clothes and hairstyles are badges of belonging for teens, as well as a chance to exert some measure of independence and individuality. Your son is especially worried about being made to dress in his father's idea of "proper" clothes because he will come under great scrutiny as the "new kid" in school. Your son does not need any additional anxieties placed upon him regarding whether or not he will fit in or be accepted by his new classmates.At this stage of high school, cliques and friendship groups have been in force for some time. Your son doesn't need to stick out like a sore thumb in his polo shirt and "proper" pants uniform at such a crucial time in his social life.
Your husband clearly personalizes how your son physically presents himself to the world. His insistence on telling your son what to wear shows that your husband has some emotional issues connected to dress and one's worth. I am hoping that this matter can be settled amicably, by asking your husband to consider the emotional needs of your son in his critical transitional year from private to public school. If you can unearth why this means so much to your husband, perhaps you can help him work through this conflict. Meanwhile, if your husband continues to order your son to dress in this manner, you can expect a growing chasm between father and son and increasing family discord. You have to be careful not to make this into a triangular conflict between you, your son and your husband. Maybe some adult friends of yours can have a talk with your husband, friends who have kids attending this public school who allow their kids to dress themselves. Keep me posted if I can be of any further help.