With a Basic (purple) membership, you will have access nearly all the different forums and sub forums that the other paid memberships have, like Political and Around The Grinder. You wont have access to some that are related to the Exchange, like the Want To Buy forums. You'd need Gold or higher for those.
Basic (purple) : Bare bones membership that allows avatars, signatures, limited attachments and private messaging. Does not allow selling in Exchange area (can trade though)
Gold: Allows you to sell in the Individual areas of the Exchange, 100 private messages, a custom signature and a 100x100 avatar. Please note: if you are a Knifemaker, Retailer / Reseller, Manufacturer or Materials provider this is NOT the membership for you.
Platinum: Platinum Membership has it's rewards! Not only do you get all the benefits of a Gold Membership, but you also are able to change your own custom title, get 5mb of attachment storage, a 120x120 avatar and storage of 300 private messages.
Those descriptions are from the following link. The description for Craftsman and Dealer memberships are in the link as well.
http://www.bladeforums.com/forums/payments.php
