Most city tours of Mysore finsih with a visit to the gardens, in order to take in the illuminations. At the far end of the gardens are the "Dancing Fountains".
The gardens were more impressive after dark, but I still wouldn't class them as a highlight. Very pleasant, but nothing more. Sorry.
On sunday nights (and Holidays too) the Palace is illuminated with more than 5.000 bulb lights from 19 to 21:00. It is a fabulous view, you cannot enter the Palace at night but can go in the gardens and enjoy this beautiful show…
On Sunday nights, and during festival, the palace is lit up by an amazing 5000 lightbulb. A truly magnificent sight, and worth planning your trip around.