There are a lot of threads aboiut this. You could search the boards. It is a complex issue. The general view seems to be that dark purple is not good, because it probably means you have not drunk enough water and so your pee is too concentrated. Are you drinking about 2litres a day?

It is true that you can show purple and not lose weught, and vice versa. I have found them comfort blankets in the past, but have decided to stop using them and get better at knowing for myself.

However, it must be disappointiing not to have lost anything. I suggest you write out a typical day's food and see what people think.