As much as I have to agree, I can kind of see where they were going with it. They're all supposed to be inverted versions of the mane 6, and most of them are complimentary colors of their respective elements. The only exceptions are Red Velvet, who still acts similar to pinkie pie and therefore, on the surface, isn't really a whole lot different. This kind of corresponds with the whole 'fear' thing, as something cute and innocent on the surface is actually a psychotic monster on the inside. Starlight shadow doesn't fit the color inversion theme either, but I can't really put my finger on why that is.