Celeste is Bianchi's official color. If I remember correctly, it has changed over the years. I remember seeing a very old Bianchi celeste that looked blue rather than the current green color.
Here is a Bianchi advertisement:
Here is my 1983 Specialissima:
I thought there would be a noticeable difference. But it does not look different at all. So I looked it up on Wikipedia and found this - Celeste (color).There has been variation over the years.