Since some years i am working on monochrome graphics libraries for the Arduino world (dogm128 lib, U8glib). I got a lot of requests to add support for true color displays to U8glib, however U8glib has been optimized for monochrome graphics and does not really allow true color displays. So i finally ended up in creating a new library (mostly based on the algorithms and concepts of U8glib): Ucglib. I added support for some of my color displays and optimized everything for color displays.
did you connect the -3,3 V for the contrast power correctly ?
And even more difficult, the display does not provide a negative power output. You will need an external negative voltage converter (see top of page 3).
Additionally the Backlight LED requires an external resistor. According to the datasheet: Forward voltage Vf = 3.3 V Assumed Operating Voltage V = 5V (from Arduino) Max current: I = 45 mA This is: R = (V - Vf) / I ~ 47 Ohm, so i suggest to connect the backlight via a 47 Ohm to the 5V of the Arduino. Well, it might be already damaged if it had been connected to 3.3V directly.