Ferdinand Bauer (1760-1826), Austrian botanical illustrator, created this Colour Chart for his field observations.

He would sketch a black-and-white drawing of a specimen in the field and note the corresponding colours from this chart, paint-by-numbers-style. Later, he would paint in the colour when he returned to his studio.

Bauer’s paintings of Australian plants are amazingly accurate. Before the age of photography, natural specimens had never been shown in such precise and realistic detail.

http://adb.anu.edu.au/biography/bauer-ferdinand-lukas-1754