Harunobu certainly was not the first to make the step from black and white to multi-color prints (Moronobu was the first artist in the world to make color prints). Harunobu was the first to take full advantage of this new technique, and he made the Ukiyo-e style popular. The need to produce multi-colored prints was a result of market demand. There were at the time only two ways to produce multi-color prints: either to print it in black and white and color it by hand, or to carve an additional block for each color. The Japanese chose the latter; Europeans chose the former.
We have the entire Harunobu Fukkoku collection on our site.