The flower is sacred to Lord Shiva and is offered to the deity. The Arali tree is the sthalavriksha at the Shiva temple at Tirukaraveeram, Tamil Nadu. The presiding deity here is Lord Karaveeranathar. The flower is also sacred to Lord Vishnu.
Although, red flowers are normally considered auspicious to be offered to Hindu deities, especially to the Devi, with Oleander(lotus and rose)all colours are equally acceptable.