You find such great value in XP as you explore the depths and airs of Minecraft, so add a little rainbow assorted mixes to the color selection of your XP. By letting the XP breathe in various random colors, as opposed to that singularly murky boring green, you add easy variety and color to the world.
So why is XP that same green color? It looks like puke, and you end up seeing so much of it. For consistency (and a lot of it) there is a bit of value. But the rainbow XP mod for Minecraft adds a wide assortment of colors, randomized from 1-100. The algorithm is slightly complex, but what you need to know is that it is designed to change colors frequently and evenly, so you get a nice distribution of color choices. it also accounts for shades of certain colors, and uses a two-step code to make sure even these are distributed nicely.
You see such a high influx of XP, and the same boring green simply does not cut it. At its simplest level, the rainbow colors add variety and freshness that was missing. In that way, it could be one of the most organically valuable mods the user base has to offer. Not every mod is pure comedy, and not every mod is innately useful. But be assured, the rainbow mod is something you never knew you needed, but once you have it, you will never go back.