The festival of colours, played on the day after Holika Dahan on Phalguna Purnima.
Holi marks the arrival of spring and the triumph of devotion over evil — the burning of Holika and the protection of Prahlad by Vishnu. In Krishna tradition, Holi celebrates the playful colour-throwing between Krishna and Radha in Vrindavan.
Holi is observed on the civil day where Phalguna Shukla Purnima is present at sunrise — the day after the previous evening's Holika Dahan (which itself is performed during Pradosha Kala on the Purnima).
Computed for Soho (Europe/London) using local sunrise, sunset and astronomical positions.