Change color of bars on hover in bar chart

Hi all,

Thanks for all the great work you do here. I would greatly appreciate it if you could help me with hover. I have created a bar chart using trace0 = Bar etc. I need to find a way for the bars to change (not permanantely) color on hover. I have 9 yellow bars, and I want on hover the bars to lighten up. I have tried the on.hover callback but I can not get it to work.

Any help would be greatly apprieciated!
I am coding in Python Jupyter notebooks, and th documentation on hover events is sparse.