Black roots look great with a light blonde balayage like the model in the picture. Color your long bob in a dark ash blonde near the roots and add some platinum baby lights at the ends.
Light Blonde Balayage And Dark Roots Inspiring Ladies https://www.inspiringladies.net/light-blonde-balayage-and-dark-roots.html
The New Platinum Blonde Is Hereand Its The Only Hair Inspiration https://www.southernliving.com/fashion-beauty/hairstyles/platinum-blonde-hair
Kryssma Fashion Ombre Blonde Glueless Lace Front Wigs Dark Roots Side Part Long Natural Straight https://www.amazon.com/Kryssma-Glueless-Resistant-Synthetic-Replacement/dp/B01MQYAERD