INHO, color filters are a
want to buy not a
need to buy. When using an external strobe the backscatter is much less than with the cameras internal flash, so if you do not have an external strobe yet that is more important to taking better photos overall than a color filter. Another route to go is a wide angle lens (requiring the port adapter for your housing). Then you can get closer to the subject so there is less suspended particles between camera / subject, although internal flash is not workable with most wide lens set ups.
I have both a tropical filter for my PT-015 housing and one for my Inon WAL but they have not been in the water in years. If the goal is to make the pictures look like it looked to your eye at the time, photoshop will still most likely be required for the ambient light photos. Why fiddle with taking the filter off every time you want to use the flash or strobe during the dive, if you will spend at least the same amount of time in front of the computer after the dive?
The Molokini dive is one of the most challenging photo dives I make, mainly because of the time of day. The deep dive is very early, the sun is just barely over Haleakala, and if you are doing the backside you are mostly in shadows to boot. If I was doing that dive a lot I would play more with manual WB, but I don't like to get up that early.
Here is a grey reef shark at ~60' on the early dive near reef's end.
This was shot RAW/Auto/P with WAL and then PS'ed. Perhaps a tropical filter would have helped.
The full gallery may be seen here (not sure, still in smugmug trial). Slideshow not working well as it blows it up beyond original size. Figured it might be consistent with Gilligan's photo display probs.
halemano : photos : Molokini04_25- powered by SmugMug
The eagle ray moves from ~50' to ~70', grey at ~60, garden eels below 80', white tip ~70', trevallies 40-50 but I was closer.