You, as a proud Filly, are most likely permanently connected to one of five magic colors: Pink, Dark Pink, Yellow, Green and Blue! The magic color does not affect your body, mane, tail (typically), hoof or eye color; however, your magic color and the color of the crystal in your possession must be the same color.
If you want to pick the Special color, then too bad, you can't! The Special color is reserved for, well, special characters: Crystal, Magic, Sparkle, Jewel, Abra, Cadabra and others. But if you really want to break the rules... as a Special Filly, you would have five crystals in your possession, one of each color.
There is quite a number of exceptions to this rule, though! There are fillys who do not tap into the Filly Rainbow and have all sorts of different body colors. But here are the rules that the majority of the known Filly population lives by.
If you are a Unicorn filly, like Rose, your magic crystal is embedded into your crown, and your magic color also dictates the color of your horn - it should be the same color.
If you are an Elf filly, like Bella, you have to wear an additional piece of jewelry! If you are a boy elf, you wear a bracelet on one of your front legs. If you are a girl elf, you wear a necklace around your neck. Your magic crystal is embedded into whatever additional jewelry you have, leaving your crown nice and clean.
If you are a Mermaid filly, you have to wear either a bracelet or a necklace, just like an Elf filly would! However, this time, the magic crystal is in your crown regardless of which accessory you wear. Also, your tail is the same color as your crystal.
If you are a Witchy filly, like Lynn, you get to have your own cape, attached to your necklace! The cape is of the same color as your crystal, and the crystal itself is in the necklace, leaving your crown neat and tidy. In addition, your cape has patterns in accordance to the theme of your magic color - hearts for Pink, flowers for Dark Pink, fire for Yellow, wind for Green and water for Blue.
If you are a Butterfly filly, like Alyssa, your magic crystal is in your crown. And also you get a pair of antennae sticking out of your head - their color matches your crystal color! Your huge butterfly wings don't have to match it, though their pattern should reflect the theme of your magic color - hearts for Pink, roses for Dark Pink, suns for Yellow, leaves for Green and water for Blue.
If you are a Star filly, the Filly Rainbow works slightly different for you: there is no Green color to choose, leaving you with Pink, Dark Pink, Yellow and Blue. Your horn and your wings match the color of your crystal, which is, once again, in your crown. Additionally, if you happen to be a Pink Star, the base of your wings is golden, and each of your hooves gets a small golden wing - to help you fly!
If you are a Royal filly, the Filly Rainbow, again, is little bit altered for you: instead of Dark Pink, you get Purple! Your crown once again holds the crystal and, unlike the pure gold crowns of other Filly types, is of the same color as the crystal.
If you are either a Princess or a Fairy filly, you have no connection to the Filly Rainbow at all. Your still have a crown, and it still may have crystals, but you are free to choose how to decorate it. The downside? You have no access to magic! If you are a Fairy, you can still fly, but if you are a Princess filly, you are pretty much just a crowned horse. With a royal title, though!
Finally, if you are a Forest or a Beach filly, you're a horse! No crown, no title, no Rainbow - free to enjoy your careless life.
In addition, if you are a Witchy, Butterfly or a Star filly, you may be connected to the sixth color of the Filly Rainbow: the Mystery color.
If you are a Mystery Witchy filly, your crystal is purple, and instead of a simple crown, you get a witchy hat, like Abra and Cadabra! This hat is also purple, to reflect your mysteriousness; however, your cape is green! Even though the patterns (which are now leaves) on your cape are still purple.
If you are a Mystery Butterfly filly, your crystal is purple again, your wing pattern is... butterflies! However, your antennae may be any of the other five magic colors. Does it mean you are both a Mystery and a non-Mystery filly? Who knows! It's a mystery!
If you are a Mystery Star filly, your wings and your horn are typically deep blue.