If you want to improve the color/lighting of XIV, you'll want a Reshade of some form.
Plenty to find on the Mod Archive though. Since other people won't see your outfit it's for personal satisfaction and screenshotting, while I like to get gear to show off to other players.
Moogle Maps ( ) will change your in-game maps to show all the Treasure Hunt and Hunt mob locations.It is the premiere UI mod for XIV though. I used to use it too, but for now it doesn't play nice with the HD UI added in 5.5, and I prefer HD icons and stuff to the color scheme they use. Many users find it clean compared to the base UI.
It's gotten a lot better in recent months and it's much rarer that you bork your install and have to start over.
SpecialSpellTimers - WeakAuras for XIV, but it's a very manual process.Also has a pretty robust community repo of prebuilt things. Can do things like press buttons for you, or overlay graphics on your screen based on certain conditions (Basically WeakAuras). Triggernometry - Arbitrary code execution based on events that happen in the XIV battle log.Will start an argument in The Balance whenever you bring it up. Also has other useful plugins such as cause of death and Eureka plugin trackers. Cactbot - Gives you DBM/BigWigs style warnings and timer bars in raid content.Everything else in this section is basically a layer on top of ACT. ACT - The damage parser, first and foremost.This is a big rabbit hole to go down! Here are the basics: