IR or red will give a light appearance to the skin depending on the strength of the filter.
It gives a wonderful fey, ghostlike effect.
Goths and similar types love it. It lightens lips and the red in the eyes.
On the other hand anything bluish will stand out. Dark under the eyes, veins and contusions will stand out. Especially with direct flash.
Eyes, brown too will get really dark. Which also contributes to the demonic effect.
Blue and UV sensitive film (essentially all) will make anything red or brown turn black or dark. Especially melanin spots right under the skin.
Black people look wonderful on it. But not all like the look. It makes white people look “old fashioned” and worn.
A purple filter (both red and blue) can be an interesting choice for portraiture. Essentially the opposite of a green filter.