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LED lighting technology is ever changing.
Some of the newer LED Christmas lights have a light output more like filtered incandescent, especially the red lights.
Until recently, red LEDs were made of a semiconductor material that emitted red light.
Some recent production uses a blue or violet LED coated with a phosphor that emits red, or sometimes yellow or green light when excited by the shorter wavelength blue or violet light. A little of the blue or violet light tends to leak through the phosphor coating and thereby gives a less saturated light.

An attractive purple colour is obtained with a thinner coating of red phosphor that allows considerable blue light to leak through and mix with the red.

The newer types of red LED may be recognised when unlit, e.g. on the retailers shelf. A red phosphor led will have a red or pink colouration when not lit. The older type will be completely colourless when not lit.