When were blue sharpies invented?

Sharpies are a brand of markers manufactured by Sanford, a subsidiary of Newell Brands. The original Sharpie marker was invented in 1964 by Sanford employee Richard Binney. The Sharpie brand has since expanded to include a variety of markers, pens, and highlighters.

Regarding blue Sharpies, the exact year of their introduction is not publicly available information.