Poundland in the UK always seem to have quite interesting little strings of Xmas lights. Last year they had a version of the fairly recent type where surface mount LEDs are bonded to lacquered copper wires and then dipped in resin to make a robust parallel string of lights. The moist interesting feature was that they had used mostly blue LEDs with a layer of phosphor to make a wide range of colours including a creamy yellw, purple, red, cold white, bare blue and finally bare green LEDs. However the green LED had a slightly lower voltage than the rest of the LEDs, so instead of getting dimmer consistently with the reducing battery voltage the other colours tended to dim out quite quickly leaving the green quite bright.
This year (2014) they have introduced a different type that is probably easier to manufacture because it just uses white LEDs, but dips the soldered LEDs in different coloured resins to provide four colours (red, yellow, green and blue) by colour subtraction filtering. The result is nice consistent intensity that should remain very even as the batteries discharge. The slight downside is that the use of colour subtraction filtering makes them less efficient, but it's a very neat development in these LEDs.