What does it mean if a guy starts to tell his lady that she should switch up her clothing style ? Is that a sign of controlling?

Is he making her change or suggesting other options? Does he accept her rejections of his suggestions or does he double down and become confrontational?

I tried fro years to get my wife to expand her clothing color palate. She didn't at that time, she would simply return anything I bought and change it for another dark plain item. Her choice. I didn't push it, eventually I stopped buying her cloths is all.

maybe , but sometimes it is healthy in a relationship to express your comments about each other . if this works both ways

Also the suggested style should be suitable for your

Yes it's controlling. Wear what you want.

it might be but perhaps she needs to get some new clothes.