Not sure it it counts as makeup but it is cosmetic, so I'm going to mention it anyway.
I can't go without my hair, lash and brow dye.
I lost a lot of pigment from my hair at a young age and have been dying it all (head, brows and lashes) back to my OG dark brown for a very long time now. Without the dye my hair is almost the same shade as my skin, and the complete lack of contrast it has with my face just looks really, really weird.
Dye is also great because living with chronic fatigue issues sucks and at least with dye, I can catch my reflection even on bad days and still see myself in it, as opposed the the undefined beige blob my head would be otherwise.