I just took a pen off Ebay that is advertised as a Waterman 7, keyhole nib, correct furniture, and a very iffy "7" imprinted at the end of the barrel. It has a purple nib.
But it has no color band at the top.
I have two 7's now, a black celluloid and an emerald-ray. The black has a disk, and the ray has nothing (both red nibs). Is it possible this ripple is a late make at the time of the ray celluloid and they didn't do the color band on them?
From the pictures, it doesn't look like there was ever one before.