From the
greek for "to call a fig a fig, a trough a trough".
First recorded english usage of "to call a spade a spade" is in 1542.
In Plutarch's time this was a pejorative. Today the term connotes
speaking plainly. However due to modern use of "spade" to refer to
people of color, the phrase is often taken as racist.
References:
http://www.alt-usage-english.org/excerpts/fxtocall.html
http://phrases.shu.ac.uk/meanings/83700.html