Technology - There are two main screen technologies currently used in phones and tablets: LCD and AMOLED. The former usually features a light source and liquid crystals, while the latter is based on organic light-emitting diodes.
Newer LCD variations like IPS-LCD and Super-LCD allow for very accurate color reproduction and very wide viewing angles, where no significant image quality loss is observed.
Current AMOLED screens differ in such a way that they can exhibit much more saturated colors (sometimes too much) and incredibly high contrast levels, which is due to black color being completely black in AMOLED displays.