Thrikkakara Appan is a clay pyramid structure which represents Vamana, an incarnation of Lord Vishnu. Onam celebration symbolises this unique structure and it is also known as 'Onathappan'.Creative Commons/Sanjith Chungath 
Onappottan is a symbolic representation of Mahabali. Onappottan in his traditional costume visits houses in the northern part of Kerala and gives blessing.Creative Commons/Nidish K Viswanathan 
Pookalam is an artwork in which beautiful patterns and designs are created with flowers on the floor in courtyard. Traditionally, it is prepared on all the ten days of the Onam celebration.Reuters 
Sadhya or Onam feast is an important part of the festival. Around 26 vegetarian dishes are prepared for the feast and it is served in banana leaves. The lavish treat includes Kichadi, Pachadi, Puliyinchi, Parippu, payasam and many more delicious dishes.Facebook/Onam Festival 
Vallam Kali or Snake Boat Race is a major tourist attraction of the state. During the boat race, paddled longboats (traditional boats of Kerala) have to compete with each other.Creative Commons/Arun Sinha 
Thiruvathirakali is one of the traditional dance form performed by women during the festival. It is a slow and a graceful dance style presented by the females in a circle around a lamp.Reuters 
Pulikali (Tiger Dance) is a colourful folk dance form performed in Trichur district of Kerala. The performers get painted like tigers in bright yellow, red and black colours and they move with the rhythm of Chenda and thakil. It is also referred as Kaduvakali.Reuters 
Kummattikali is the popular mask dance of Kerala, which is mainly performed in Trichur and Palakkad districts. The colourful masked performers entertain people by visiting houses and they also collect small gifts.Creative Commons/Aruna 
Onathallu is one of the dying traditions in Kerala and is celebrated mainly by Nairs of Pallassana Desham in Palakkad district. It involves an enactment of warlike scenario, wherein large number of men gathers together and tries to beat each other.Screenshot/Youtube
Onam, which is an annual harvest festival of Kerala, has created a festive mood in God's own country. The festival is mainly celebrated by Malayalees around the world with traditional folk dances, artworks, etc,.
According to the Onam story and its popular myth, Lord Vishnu in his Vamana avtar sents King Mahabali to hell as the gods become jealous of his popularity. But grants him a boon that the king can visit his subjects once in a year. Thus, it is believed that Onam is celebrated as King Mahabali's visit to the place. It is the only festival in which both the winner and the defeater are worshipped.
The harvest festival brings many colours with it and thus celebrated in a grand way in Kerala. From 'Atham' to 'Thiruvonam', it is a celebration of ten days.
Check out the above slideshow of Onam Celebration and its different colours.
