The test for blue is to know a pretty extensive amount of techniques, and then to do some sparring.

Purple - no techniques to know, but a lot of sparring. You must also be able to show combinations of techniques, i.e. chaining moves together, rather than doing techniques discretely. I've seen people who can do techniques well, but not chain them together, fail. A lot.

Sparring for purple is positional. You start from guard, mount, and side mount - all of those offensively and defensively. So you do six rounds total, with however many people show up. And generally you go with each person about 3 times each round.