Eyebrow pencil color for grey hair?

I have to use this account because i temporarily can’t get into my other one, but this question is to help my mom.

She has let herself go completely silver at my suggestion and I think it looks great! But she has almost no eyebrows at all due to some conditions. Her dermatologist has suggested Microblading, but that has its issues. Even if she wants to do that, she has had so sparse eyebrows for so long, and didn’t know how to do them well, neither of us know what her natural ones would look like if they are there. I have started using a individual hair stroke style pen on my brows and have loved how natural it looks and it’s so easy, I have suggested my mom start using one of those and see if she still wants Microblading, or at least to practice how she wants them to look before they are permanently tattooed on her face because bold, 2016 style brows that many microbladests do would look terrible on her.

I am trying to buy the type of product I am using as we both need super simple “for dummies” make up, and I have naturally much darker hair than her, but I don’t know what color to get. Something that would match her OF color, which is a light auburn? I have seen they have straight up grey brow pencils, but not on the form I am talking about, and I think that would be weird.

Yeah, so if you wanted to draw a light, natural looking brow on someone with shiny silver, not white hair, what would you use?