Why you wear black dress in winter and white in summer?

Being truly honest, I'm not really sure. White is always seen as a much more pure and beautiful colour and summer is thought of as pure, and beautiful month. Winter is seen as a much more cold, dark month (WHICH I DISAGREE STRONGLY WITH) and this is portrayed in the fashions which are created.

Overall, the designers have the main say as to why the 'stereotype' is white=summer and black=winter

Hope this helps :)