Indian weddings run over several events, each with a different dress code. Here is a western-wear answer for each of them.
A midi dress or a co-ord in a solid colour reads as respectful without disappearing. Keep the hem below the knee and the shoulders covered or layered.
This is where a gown or a well-cut party dress belongs — heavier fabric, some embellishment, and a length you can dance in.
Jumpsuits and co-ord sets work best here: festive, easy to move in, and far more comfortable across a long evening than anything with a train.
White or ivory at the main ceremony, and anything so fitted that sitting through a two-hour function becomes the main event.