Come March, we will see from Iwako, Series Two Duck Japanese erasers. In this second series of duck Japanese erasers, green and orange are the two new colors that were not in the series One Duck Japanese erasers.
The blue, yellow, purple and pink are different shades of their cousins in the Series One Ducks.
We do not know how Iwako picks the colors of their Japanese erasers other than that they are pleasing to the eye. But we have to wonder why, with an infinite array of colors, why they would pick colors that are only couple of shades removed from the previous series.