This sounds like something that required layers. If so, you need photoshop or another editing program as well as Lightroom. You can fiddle with the sliders in the split toning section of LR - it's pretty cool.Are you able to just alter the color is certain areas with lightroom? On a different thread there was a picture of a barracuda and a wreck at different distances and one was able to alter the color/tint/etc at the barracuda and adjust it to a different amount on the wreck.
Hopefully it's done underwater, in camera. Higher shutter speeds will give you a deeper blue than slower shutter speeds. It's all about balancing your light from all sources to get the effect you want. Read lots of threads, the Sticky and any books you can lay hands on (in the Sticky there are quite a few listed so it's a good place to start).Also I see these pics with deep blue backgrounds. Is this a photoshop alteration or is it the skil/equiptment/luck of the photographer?
It can be done in Photoshop etc, but it rarely looks very good, imho. I'd imagine it also takes a tremendous amount of time - I'm just not that interested in learning that much Photoshop LOL