When it comes to colors there are a few color harmonies that work with a red and white cutie mark..
Might be going in to too much details, but i may as well..
If you wanted to go with a complimentary colors sceme, teal/light blue could work.. It'd also suit it considering the magic aura is electric blue
If you wanted to go with a triatic color scheme you could have the coat a deep blue and the mane a shade of green.. or vice verse..
Though most characters color schemes in the show tend to keep to a monochromatic scheme (1 color, but in different shades, contrast) or an analogous scheme (3 colors next to eachother on the color wheel, again, in different shades and contrast..)
I personally think it'd look good as a pale yellow or tan color, kinda like Vinly Scratch.. the mane could be maybe be a shade of red (Not too vivid) to match your mark.. or maybe light blue to match your aura?
Well anyways, hope this helped ⁿ-ⁿ