fresh
紑 centers on freshness, likely describing the bright, clean appearance of newly made or washed fabric.
紑 combines 糸 (thread) with 不, which may contribute a sound element. The exact historical development is uncertain.
Thread 糸 that is not 不 yet used looks fresh and bright, like a new spool of silk.
For フウ, imagine a fresh breeze (風, ふう) blowing through clean fabric: 風 -> フウ, and the fabric stays fresh.