Thanks for your observation! The greyscale values were designed to meet the needs of UI designers for both light and dark modes, with a tighter grouping at the lighter end (from 25 to 200). However, as you move towards the darker values, they become more spread out. So while there is some clustering in the lighter shades, it’s not as pronounced at the dark end. The sigmoid pattern you noticed seems to be purely coincidental, but it's interesting how such patterns can emerge!