It's a fact: no other place on planet ocean is as colorful as the coral reef. This ecosystem is literally bursting with the vibrant colors of corals and fishes - and an occasional diver in a bright yellow-and-pink wetsuit.The challenge for underwater photographers is capturing all this color on film. Here are seven tips to help you meet the challenge.1) Dive shallow. Water filters out color selectively, beginning at about 10 feet. As you dive deeper, you lose colors in this order: red (10 feet), orange (20 feet), yellow (50 feet), green (50 feet) and blue (150 feet). All depths are approximate; precise depths depends on time of day, water clarity and weather conditions.So, when shooting natural-light pictures, dive shallow. In addition, dive between 10 a.m. and 2 p.m., when sunlight has maximum water penetration.2) Shoot close. Water is about 800 times denser than air. As camera-to-subject distance increases, the sharpness and the color of your subject decrease. For natural light pictures of reefs and divers, a wide-angle lens lets you get up-close and personal with your subject. For optimum results, use a 12-mm, 13-mm, 18-mm or 15-mm lens. The wider the lens (a 12-mm lens is wider than a 15-mm lens), the closer you can get to your subject.3) Use a strobe. A strobe can show the true color of a subject. Notice that I said ''can show'' and not ''does show.'' Here's why: If your subject is beyond the range of the strobe, your subject will not only be too dark, but it will also be off-color. When framing a fish, diver or reef scene, be sure to check the subject-to-flash distance, and be sure that it's within flash range. If it's not, move in (or zoom in) closer. Rule of thumb: As the price, size and weight of a strobe increases, so does its maximum flash distance. (I can tell you where the expression ''rule of thumb'' comes from if you are interested; just e-mail me at [email protected]).4) Choose your slide film carefully. Want to show the true color of some exotic species of fish as well as its surrounding habitat? Then use Kodachrome 64 slide, known for its accurate color rendition of a subject. If you are after pictures with vibrant and enhanced colors, however, then choose one of the new extra-color slide films, which produce images with saturated and warmer colors. Another tip: Try underexposing your slide film by 1/4 stop for increased color saturation. Example: expose ISO 50 film at ISO 75, 100 film at ISO 125, etc.5) Improving Poor Prints. Got dull prints? Well, there's a chance that your lab did not do its best job. Take your questionable prints and negs back, and ask for a remake (most labs do this at no charge). In most cases, the lab can deliver a darker, lighter or more saturated set of prints.6) Dive into the digital darkroom. Digital imaging programs like Adobe Photo Deluxe and Adobe Photoshop make it easy for you to improve, enhance and manipulate the color of your picture - or an individual subject in a picture - in the digital darkroom (your computer, imaging program and printer).How do you get your pictures into your computer? Well, you can scan them yourself, have them scanned by a pro lab or, if you shoot prints, order a Picture CD when you send in your film for developing.7) Look for color. My last tip is actually the most obvious one: Look for colorful subjects! A picture of a yellow butterflyfish will have more color than a picture of a flounder blending in perfectly with white sand. Think and compose for color!As always, please remember: Take only pictures, leave only bubbles ... and only touch your shutter-release button, not the fragile corals.Rick Sammon's colorful pictures can be seen in his 20 books, on his Web site: www.ricksammon.com, and on the Web site for his conservation organization, CEDAM International: www.cedam.org.