If you like a splash of yellow in your tank, the Yellow Coris Wrasse is a nice choice. As it picks through the rockwork and corals, it will consume some pests too. As it ages and increases in size, it may eat some snails in addition to the normal food offering. This is a known jumper, so cover the tank as well as the overflows, as it may travel south into the sump.
The brightly colored Clown Goby - Gobiodon okinawae - was a great favorite of ours. It swims about, but also perches on hard or soft corals, mushrooms and LR. This petite yellow fish is a great addition to most tank. Ours lived for about 4 years before it died, but during those years, it evaded the jaws of a Lionfish for many days!! (Mysteriously, the lionfish vanished while I was out of town. Hmmm.) The Clown Goby is mostly Reef-safe, although it may damage some SPS like Acropora milleopora. The green version is a better fit for SPS systems.
For a nice dose of color, you might consider a Threadfin Anthias - Nemanthias carberryi. They love to shoal together, and having a harem in captivity is quite possible. Only one male should be with the harem (four or more), to avoid any fighting. This fish has a high metabolism and needs to eat frequently, two or three times a day, and needs very good water quality. This was my third attempt to keep this fish, and was a keeper. (The previous two died almost immediately upon being added to the tank, possibly due to acclimating too slowly.
My 55g tank came with flatworms. Some suggested a Six Line Wrasse as a natural predator for these small rusty pests, but alas, mine didn't seem interested in them. However, it added beautiful color to the reef, and disturbs nothing. I purchased it when it was very small, and no-one could get over how large and fat it grew to be. This fish may be Reef-safe, but some report how overly aggressive it can be toward other tankmates. The Four Line Wrasse might be a better alternative.
An interesting fish with lots of color is the Royal Gramma Basslet - Gramma loreto. It tends to find a spot it likes, and defends it against intruders. This fish doesn't actively swim around in the tank, except during feedings. The difference between this fish and the Purple Pseudochromis is that the colors of this fish merge or blend together, while the other fish's colors do not. Reef-safe.
Won in a raffle at our meeting, a 1" Regal Tang- Paracanthurus hepatus - quickly felt at home in our 55g reef. Also referred to as a Hippo Tang, its main diet is vegetation. It will consume some algaes in the reef tank, but needs to be well fed. Prone to ich, keeping water conditions stable will help keep this fish stress-free and its immune system strong. Feeding with garlic helps. These tangs grow quite large and need large areas to swim, so a 6' long tank (or greater) would be best.
Look at this stunning image by SveinAntonsen
The Psychedelic Mandarin - Synchiropus splendidus - is one of the prettiest fish in the reef. Slowly moving over the rockwork, they seek pods to eat. It is mandatory that the tank be established for 6 months first, and have at least 75 pounds of LR to support this fish's diet. A refugium provides excellent breeding grounds to provide even more food for this delicate creature.
I love all clown fish, but the True Percula- Amphiprion percula - is my favorite. The way they swim and stay in place remind me of Orcas, and upon entering the hobby I bought a pair. Their beautiful orange and white bodies moved together, never straying apart for long.
After seven years in the hobby, I was been rewarded with the sight of Clownfish eggs in my reef tank. What makes this story unique is that the parents are not even the same species! The larger female clownfish (near the eggs) is a seven year old True Percula, and the smaller male clownfish (above the eggs) is an A. Ocellaris (False Percula) that is only one and a half years old. For some reason this unlikely match has not only accepted one another and have been a pair for a year, but continued producing eggs about every two weeks.