The green color is so common that others easily notice different colors. The procedure is easy for an experienced electronic hobbyist. This has not been tested with any blue or while LEDs. Although the author succeeded in the operation described below, no guarantee can be given for the instructions. Opening and soldering components in a mobile phone contains always a risk to damage the equipment seriously.
Electrostatic discharge can damage the device without any visible handling mistake.
Both groups are driven separately with a transistor connected between the cathode and the resistor of the LEDs. This is a rather low voltage for many blue LEDs. These LEDs may be replaced with standard 0805-size LEDs, if they are soldered on their sides. The keyboard LEDs are of size between 0603 and 0805. They are soldered normally.