etymology - What is the origin of “call a spade a spade” and does it have racial connotations?

This is answered fairly clearly by the etymonline entry for spade:

spade (1)
"tool for digging," O.E. spadu, from P.Gmc. *spadon [...] from PIE *spe- "long, flat piece of wood" (cf. Gk. spathe "wooden blade, paddle," [...] To call a spade a spade "use blunt language" (1540s) translates a Greek proverb (known to Lucian), ten skaphen skaphen legein "to call a bowl a bowl," but Erasmus mistook Gk. skaphe "trough, bowl" for a derivative of the stem of skaptein "to dig," and the mistake has stuck.

The item before that in etymonline mentions

spade (2) ... Derogatory meaning "black person" is 1928, from the color of the playing card symbol,

an unrelated meaning.

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• Previous antonyms - Are there other words which share the prefix "ig" to mean opposite, such as ignoble?