"The message is an absolute disaster. It's racist," said Moha Gerehou, a journalist and anti-racism activist in Spain.
Correos said it had collaborated with the country's leading anti-racism NGO, SOS Racismo, on the project, but the organisation denied having any involvement in the campaign.
SOS Racismo said in a statement that the "unfortunate" Correos campaign "underlines the need to create greater anti-racist consciousness in Spain".
"Racism is not just about skin colour, but a systemic and historical problem constructed to give ascendancy to some sectors of society and downgrade others," the statement continued, accusing Correos' campaign of perpetuating the idea of a hierarchy of races according to skin colour and exhibiting "negrophobia".
A spokesperson for Correos told The Telegraph that stocks of the stamps have been exhausted due to high demand, and that the "campaign is now over".
A promotional video for the Spanish Tourism Ministry's recent relaunch of the country as a tourism destination aimed especially at British and other European markets titled "You deserve Spain" failed to include any Black or Asian individuals or families.
"Maybe they don't deserve Spain," one journalist wryly commented at the launch.