It sounds like the OP doesn't post-process photos, just shooting jpeg and using the camera image. If that is the case, having a true color target isn't going to help much.
You might check to see if your camera has a "picture setting," or whatever your particular camera manufacturer calls it, for underwater shooting. The object would be to offset the blue shift caused by the water. If all else fails, I might try setting the camera for sunset, which should redden up the images a bit, or use the custom color setting to shift the Kelvin temperature to the red a little. If you won't be adjusting the images after the fact, it will probably come down to trial and error.