Hi.
You can use lightweight mode to have pixel-perfect fonts, but only if you are running virtual sessions.It can be enabled in the Server preferences -> Performance tab, accessible by clicking on the “Show the server status” button of the tray icon on the server (or by editing the “AgentLightweightMode” key in the ‘/usr/NX/etc/node.cfg’ file).
As explained by titan in the post above, work is in progress to provide a lossless RGB mode in all types of session.