I do shoot raw. In lightroom I like to use the dropper tool and pick something I know is white, but sometimes in a shot there isn't anything to pick!!Just a suggestion to save you a lot of money and time buying this and that just to solve a simple problem:
1. If you're using LED's, why not turn the color dial to a point that's more on the side of white light?
2. If you're not using LED's or adjustable color lights, as saltyfilmfolks suggested, bring the Kelvin temp as high as it'll go, also, I hope you're shooting raw, go to lightroom, it doesn't matter if its blue, you can still set a reference point on what is supposed to be gray. Then manually adjust. Or just manually adjust from the start.
You dont need filters on your lens to achieve this
This fish is light colored, so I can do it.