The Catechism Of The Catholic Church Part 3, Section 2, Chapter 1, Article 1, IV explain the question between the images and the First Commandment.
Also it explains about the characteristics of the angels here Part 1, Section 2, Chapter 1, Article 1, Paragraph 5, I.
Knowing that, you can understand that the Angels, as completely spiritual beings don't have defined physical forms. In their appearances through the Bible and all History they assumed different looks.
So, representing them as winged humans, with curled, long, or short hair, and any skin colors are artistic representations. But at the same time, they can appear just like those expressions or any other.
Additional info: since most of medieval and renascence sacred arts were made by caucasian Europeans, it makes sense that their representations look like them. But there are lots of images of the Virgin Mary as African, Japanese, American Native for example, that were made by them. So goes the angels.
I'm brazilian and at my city's Cathedral there are an painting of Christ resurrected surrounded by angels of all ethnicities.
I hope I explained enough!