This is a mid-19th Century chromolithograph by Casimiro Castro, showing a view of the Metropolitan Cathedral, in twilight. Up close and in person the print is a glowing grayish blue.
The image above is from the NYPL Digital Library, via BibliOdyssey, which has lots more links tagged Mexico to really wonderful historical prints. You can examine many of them up close at the permanent prints drawers at the Museo Nacional de Arte or in temporary shows that pop up at the Museo de la Ciudad de Mexico. Some show "villages" that are now complete engulfed by the metropolis: Iztacalco, Iztapalapa, Tacubaya ...
* Enjoy.