In 1772 the first patent was issued in England for making coloured inks, and in the 19th century chemical drying agents appeared, making possible the use of a wide variety of pigments for coloured inks. Later, varnishes of varying stiffness were developed to make inks for different papers and presses.

When was blue ink first used?

Prussian blue was discovered in the 1700s and indigo even earlier. However, blue writing inks show up on American letters in the 1830s, probably not much before 1838, from which I have seen several examples. By 1839-1841, they are common, having been used by postal officials at many offices. These blues are acid inks.

What Colour was the first ink?

Ink is typically colored, but the very first inks used charcoal or soot from the fire as the main pigment, hence why most of the early written works found were written in black ink.