I followed instructions mentioned here and installed the Color Ramp Manager by choosing install experimental plugins as well.
Now, when I go to Properties > Style > Single Band PsuedoColor and I choose New Color Ramp > Cpt-city > This empty box opens up.
How do I hillshade my region?
Current QGIS comes with cpt-city color ramps, that is probably the reason why the mentioned plugin is no longer maintained.
Uninstall the plugin. Then you will see the option to choose cpt-city sets when you click on New Color Ramp (as you have done).
The sd-a, recommended in the linked blog, is found in Topography group.
