The ideal food coloring to use for your cakes has to be gel based colors. Firstly the consistency is not watery but rather like a gel. So it doesn't ruin the consistency of the icing or fondant. Second they are really strong colors. A few drops of it is enough to get a deep bright red. Unfortunately gel based food coloring is not available in India at least nowhere we have looked.
So we ordered our colors from Ebay. There are approved Ebay India resellers who will arrange for anything from the US to be available on Ebay India. The price they quote is in INR and they take care of all the shipping and custom formalities. Simply go to Ebay India and search for food coloring. Scroll down to the section on e-bay Global Easy Buy. You will find fantastic products including air brushing kits and various food coloring accessories all available in INR inclusive of shipping.
You still have to ensure that the seller is reputed and that you are paying via secure channels. We have used the seller i2cworld and we are very happy.