I have not tried this for imperials but it works for bretons. My pale male breton became really dark as a vampire so i worked on sliders and found a few tricks

Choose 2nd skin tone from left
Dont choose last complexion or the 2 that make you look sickly(red veins on face)
No dirt
Neutral eye shadow/neutral tint
No eyeliner- eyeliner leads to dirt
Face tattoo-choose dark white tattoo that covers most of face first. Then remove tattoo and you should still see a leftover ghost tattoo. If you choose a new tattoo don't choose ones that block out eyes as it somehow darkens rest of face. I went with black cheek tattoos with no bleeding into rest of face

My breton vampire is fairly pale and doesn't look dirty (xbox no picture)

One last related point give yourself 1-2 jaw width otherwise the bottom of face will get 2 sunken in. Beards hide most of red mouth lines. Blind eyes get glitchy if you go vampire