Mazal tov on your upcoming wedding!

A spray tan is not considered a chatzitzah, because it is in place for beautification and because no independent substance remains on the skin long-term. The active ingredient in the spray is absorbed into your skin and changes its pigmentation. 

If you are planning to get a spray tan for your wedding, it would probably be wisest to immerse in the mikveh early (up to four days before the wedding, learn more here), and then get the spray tan after you have immersed.

In the future, if you plan to immerse with a spray tan, it is best to do so when the tan is still beautifying. So before immersion, it should be applied evenly (or touched up), and you should remove any unwanted stray bits of tanner (on nails, etc.).

If you plan to stop using spray tan, then prior to the next immersion you should just clean and exfoliate well, so that whatever is left looks presentable.

Please let us know if we can be of further assistance.