Four coloured tri-colour flag. (நான்கு வண்ண மூவர்ணக்கொடி)
Is it because white is not considered as a colour?
No. The wheel is not considered!
It is composed of three colours with a meaning and a navy-blue wheel in the center. Mexico and Croatia also have tri-colour flags with more than 3 colours! See http://en.wikipedia.org/wiki/Tricolour