The 510 will be available in 5 different colors... Yellow, Red, Black, Cyan and White
Here are some of the specs...
You can check out the full specs list HERE
The 510 looks very similar to the Lumia 710 in design.
Here is a nice hands on video too
The Nokia Lumia 510 will be available to buy starting in November in India, China, South America and Asia. It will cost approximately USD199, that's before taxes.
Source: Nokia Conversations