How many letters does the top answer for “author of the sword in the stone” have?

The most common answer is white (5 letters).

Crossword clue: author of the sword in the stone

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

white 5 letters wd-fact-v3

being of the achromatic color of maximum lightness; having little or no hue owing to reflection of almost all incident l

author of romancing the stone 50% similar → zemeckis

author of with fire and sword 50% similar → sienkiewicz

wrote the sword in the stone 50% similar → white