This is difficult to answer without photos or more information on growing conditions and your soil and water management.
Is this a new planting or mature. Is this the first year that you have noticed the discoloration and leaf drop, or does it happen every year at this time.
I suspect drought dormancy. In a tropical monsoon climate, this should be your dry season and beginning of the hot season. Some otherwise evergreen plants go dormant this time of year, especially if they are not watered adequately after the rainy season ends. I'm in Thailand and it happens here with some plants that are not irrigated.
I have lived in Pondy where it is never cold, but I don't know Bangalore and if you may be in a hill station where you get a low temperature spell and cold dormancy. Chilean jasmine will go dormant if conditions are such.
You know you have a great resource there with the Bangalore Horticultural University. You may be able to get local information through their extension program or ask for a referral to a landscape plant health care specialist.