Hydrangeas do well in part sun/shade in Chennai. Mine only gets sunlight for one hour in the evening, and I should say, the leaves are healthy looking and are even giving out new shoots. Evening/ early morning works best, because the sun is not too hot at the time. It is best, to let the plant be on shade the rest of the time.
Did you know you can make the flower change colours from pink to blue and back? The pink coloured flower is because the pH of the soil is alkaline and the blue colour is because the pH of soil is more acidic. You can try using garden lime to get pink flowers or coffee grounds to make the soil more acidic (in turn, make the flowers bloom all blue). Do not do it in concentrated solutions, ensure that it is very very diluted and use it sparingly. The flowers will not change colour immediately, you need to give it some days.
This does not work for white or cream Hydrangeas.
PS: If the plants grow in concrete pots / walk ways, it might be hard to make them change colours, as it will be absorbing lime from the concrete, which will make it tough to change colour.