I am on mobile, but I will try to answer your question with what sources I have.

In terms of Iberian medieval art, not all Moors are black. The works from the Castilian kingdom of Alfonso X, displays and defines "mouros" in different ways. Alfonso's own legal code, the Siete Partidas, defines Moors by their religion, and not their skin tone:

Moros son una manera de gente que creen que Mahomat fue profeta et mandadero de Dios (Moors are a type of people who believe that Mohammad was a prophet and messenger of God, Partida 5:1438).

By not referencing their external appearance or linguistic tags, Josiah Blackmore argues that "Moorishness" in medieval Iberia was "an internal quality, all the more dangerous because it is not readily apparent to the eye."

Later, the Cantigas de Santa María, a collection of religious songs patronized by Alfonso, changes this "Moorishness" to mean blackness or -- another physical cue -- beardedness. Cantiga 46 tells the story of a Moor who loots a painting of the Virgin Mary. In the panels depicting the story, the Moor--who later converts to Christianity after marveling at the Virgin's image lactating--sports a large beard, a distinct sign of his otherness. The moor then tries to convert his friends, described in the text as "estes mouros barvudos" ("these bearded Moors").

Cantiga 185 displays a black bearded Moor, this one accused of adultery with his Christian mistress. When the woman and the Moor are burned at the stake, the Christian is protected by the Virgin, while the black Moor dies in the holy flames--a sign of his lack of favor with God and the Virgin.

Black or swarthy skin in the Cantigas is reserved for some Moors (usually, the ones who do not convert to Christianity) and demons. Cantigas 34 and 125 depict the Devil and demons, all of them painted in dark blacks, greys, and blues.

Additional sources: David Bindman, Henry Louis Gates, and Karen C. C. Dalton. The Image of the Black in Western Art Josiah Blackmore. Moorings: Portuguese Expansion and the Writing of Africa.

For bonus points, I'd be very interested in whether the majority of the population looked as depicted in those paintings or had a lighter skin more akin to modern day Arabs.

Not necessarily true. Shakespeare described black people in his writings as moors. Many try to center moors to morroco when really they have history all over the world. Anything depicted with dark skin is at least 95% authentic, it's the white-washing you need to look out for. Same reason you can hardly find a black person in Egypt nowadays.