Thank you for flagging this, you're right that these skin tones aren't currently appearing on randomly generated women. This is something I plan to fix in a future update by tying it in with an ethnicity feature.
Each ethnicity will be tied to a pool of names, skin tones, hair colours/styles & eye colours, plus some other appearance options. I was then thinking of adding a city area you can explore (maybe London outside of just day trips) that will be much more diverse than the town, allowing you to meet girls of a variety of ethnicities.