From : http://www.word-detective.com
it's called Google, people. Why don't you use it before you spout off looking for racism where it doesn't exist...you go, WSEWC!

The mistaken notion that the phrase had its origins in confusion over what to call a digging implement. I don't think the phrase is quite that innocent. My understanding is that in fact "calling a spade a spade" harkens back to Civil War America, when a person's freedom turned on whether or not the establishment considered one Black or not. Inter-racial liaisons were not uncommon, and so mulatto children were reasonably common. The White establishment was loathe to allow itself to be "diluted" with "impure blood," and so they took to "calling a 'spade' [pejorative for a Black person] a 'spade'". Is there any truth in this? -- Michael Raynor.

In a word, no. Although the English language, and particularly American English, contains many examples of the influence of racism on popular speech, in this particular case there is ample evidence to prove the defendant phrase not guilty. "To call a spade a spade" not only predates slavery in North America by quite a bit but harks all the way back to the Ancient Greeks, occurring in the work of, among others, the playwright Aristophanes, and is still commonly heard in modern Greek. The original phrase seems to have been "to call a fig a fig; to call a kneading trough a kneading trough," applied to someone who spoke exceedingly frankly. Evidently, when the phrase was first translated from Greek in the Renaissance, the Greek word for "trough" was confused with the Greek for "spade," and thus the modern version was born. The "spade" referred to in the phrase, incidentally, was the digging implement, and not the black character on playing cards that underlies the racial epithet.