WhatsApp Messenger for BlackBerry 10 made a step towards an improvement I have been asking for in their app. They have added color titles to group chat bubbles so you can differentiate between parties in the group easily. Its not as nice as different colors per user as they have in the Java BlackBerry client but its a start. They also included various bug fixes including a fix for last seen status and screen scrolling.
Check out the latest version of WhatsApp for BlackBerry 10 free in BlackBerry World