BLACK

Why do we wear black or blue or kaavi dress?  

Wearing black clothes is the traditional dress to indicate total with-drawl of mind and total absorption into the "Self" or "Athma". (Objects are black due to complete absorption of color spectra). 

What is Maya? The reality is that everything in this universe is only Pure Consciousness. There is nothing other than Consciousness. Everything is Consciousness, but we make an error of seeing different names and forms. This inability or error of seeing different things and forgetting the reality, the Consciousness is Maya or illusion. In simple words to think that we are this mortal body and mind without being aware of the Awareness and Consciousness functioning in us, is Maya or illusion. The donning of the traditional black, blue or saffron clothes during the Vratam period has its own significance.

Blue: First the Lord is described as Neela Megha Shyamala Varnan.  Not only that Ayyappa wears blue Soman (Panchakacham) and He likes the colour.  Most devotees wear the Blue colored Mundu, to associate themselves with the Lord.

Black: Lord Saneeshwara is ebony black in colour. And those people (Ayyappa Swamis) who suffer from Sani Doshams, are instructed by their Guruswamis to wear black Mundus, so that they may be released from Sani's maleficent effects. Apart from this they are also guided to chant the 12 stotras that are pleasing to Saneeswara as they climb the Sabari Malai so that when the Ayyappa Bhakthas reach the top, Sani Bhagavan would have removed himself from their lives.  Also Sani Bhagavan will not come in the way of devotees who wear black colour clothes.  Ayyappa has ordered Saneeswaran like that since Saneeswaran was defeated by Manilandan while attacking Him as per Sani Bhagavan's duty.

Saffron/Kaavi: Certain Ayyappa Bhakthas who live the life of a Sanyasi within the Grihasthasrama (Guruswami), detached attachment, wear Kavi vastram including Guruswamy.

White: Those who without any self interest devote their attention entirely on Him, wear white veshtis, as they consider Him as Nirguna Bhagavan.

Wearing the colored Mundu also has the added advantage of letting the others know that you are observing the Vratam. This is especially important as it relates to letting women know, so that they can distance themselves from the males who are observing Vratam.  However, mainly it is advisable to use black/blue or kavi mundu as the case may be. In case of kanni ayyappa i.e. if the devotee is going to Sabarihills for the first time, he/she should wear only black colour clothes.