OPI Moon Over Mumbai is a sheer dove grey shimmer with a hint of lavender. I love this color because it's soft and clean without being pastel or stark like a white. It doesn't hurt that it makes my hands look elegant.
The closest colors I could find to OPI Moon Over Mumbai are Essie Great Expectations and Avon Urban Grey. The Avon is a creme and more opaque and a hint lighter. The Essie is a bit more sheer and the shimmer is a bit more pronounced. All three are a very close match.
Essie Great Expectations and OPI Moon Over Mumbai are available at TransDesign. All three can be had from Ebay for between $3 and $5.