Refer to figure.
ICAO Annex 14
5.3.7 Runway lead-in lighting systems

Characteristics
5.3.7.4 Recommendation.— Each group of lights of a runway lead-in lighting system should consist of at least three flashing lights in a linear or cluster configuration. The system may be augmented by steady burning lights where such lights would assist in identifying the system.
5.3.7.5 Recommendation.— The flashing lights and the steady burning lights should be white.
5.3.7.6 Recommendation.— Where practicable, the flashing lights in each group should flash in sequence towards the runway.

Note: even if the regulation does not make it clear, it seems that EASA is after the answer "threshold". Please let us know if you come across this question.