Wash and soak urad dal and idli rava separately.Urad dal needs to be soaked for 5 to 6 hours or overnight.Drain the excess water and start grinding the urad dal with some salt in a wet grinder or blender to prepare the batter.Add some water if needed and blend till you get nice frothy thick and smooth batter.

Squeeze out excess water from rava and add to the urad dal batter. Mix well and keep aside for fermentation in a warm place for a few hours.Boil carrots and blanch spinach separately and put it in a blender for fine puree for the colour.Once the batter is ready, take some batter in 3 separate bowls. Add the carrot puree and spinach puree to the 2 parts of batter separately and stir nicely to get the desired colour. Keep the 3rd part of batter as it is.

Take the idli mould, insert muslin cloth, sprinkle some water and keep aside. Preheat the idli steamer.With a help of a spoon, first add the orange colour idli batter in the idli mould then the plain idli batter and the third with the green idli batter.Cut one okra and place it on the centre of white layer of the idli batter.Cook the tricolour idlis in the preheated steamer for about 15 to 20 minutes.Idlis should be soft light and fluffy.Remove the tricolour idlis.serve hot with sambha chutney.