Nel's hair was meant to be this color from kubo. But since he was not involved in the original anime run studio interpreted the color as greyish blue. Now in tybw kubo is very much involved especially in character designs so a lot of things are being corrected. Another example is ichigo shikai gentsugatenahou was blue in original anime but in tybw they corrected it to yellow which was kubo's original idea
Nel's hair was meant to be this color from kubo. But since he was not involved in the original anime run studio interpreted the color as greyish blue.
Now in tybw kubo is very much involved especially in character designs so a lot of things are being corrected. Another example is ichigo shikai gentsugatenahou was blue in original anime but in tybw they corrected it to yellow which was kubo's original idea
Ah! Thank you so much for explaining :)