[Ben]

Thought a toggle on/off filter icon would well be placed in the library´s blue menu bar.
"Show Filter" icon, white colour: when clicked the filter area is shown. No filter(s) applied when icon is in white colour.
"Show Filter" icon, red colour: when clicked the filter area is shown. Filter(s) applied when icon is in red colour.
"Hide Filter" icon, white colour: when clicked the filter area is hidden

Would this make sense?
Cheers
Ben