Indoors in less lighting and/or at certain angles the Deep Purple almost looks space grey-ish, with or without this case. I don't think the matte black edges of the Spigen UH case makes much difference how the purple looks, to my eyes. Note that the case is named "Ultra Hybrid Matte Black", but the matte black specifically refers to the black edges of the case only. The back of the case is entirely shiny & clear.
Spigen does have another version of the UH case called Frost Black, I believe the back of that case is more of a smokey matte finish, so maybe that one affects how the color looks through the back of the case. I would have preferred this case came with a clear/matte finish on the back to show less fingerprints, but that combo doesn't seem to exist in this product line