I have an inexpensive underwater camera (basically a knock-off GoPro camera). This camera is sold under a lot of different makes and models, but mine is a DBPower E5000. I've used it when I go snorkeling, and it takes great pictures and video, but the color gets very washed out below a certain depth.
There are companies that make filters for GoPro cameras, but none that I could find would fit this camera. I bought a cheap filter set and decided to make an adapter to fit my camera. Below is the set I bought:
This adapter is designed to be press-fit, but since things vary on different machines and water could lubricate the joint and allow it to work loose, I included a few loops on the sides to tie a rubber band or elastic to the adapter so nothing gets loose and floats away.