If you’re interested in how people became white you can consult Nell Irvin Painter’s very interesting study The History of White People. The image below was first published during our period. Racism often relies on caricature and the use of the grotesque. Note that the figure on the right is meant to be understood as Irish. Thomas Nast’s cover illustration expresses contempt for the object of its ridicule: immigrants and freedmen.
In general, it’s better to take the time to look up terms via the dictionaries that are available through the library. This definition of the term ‘Grotesque” comes from an online source.
Cuddon, JA, M. A. R. Habib, et al (eds) A Dictionary of Literary Terms and Literary Theory