Giselbaer's Durability Viewer

Durability Viewer standard display

Durability Viewer showing your free inventory slots (31), slightly damaged bow and helmet (negative, what's missing to 100%), more damaged pick and chestplate (positive, remaining durability), arrow count (59), and undamaged pants/boots.

Armor around Hotbar mode

In this mode, the armor is shown around the hotbar, and the "percent to show damage" option is set to 100% so you'll always see remaining durability instead of item damage taken. (These options can be set independent of each other).

Color codes

The number you can use for the tooltip color corfiguration is the standard MC color code. User ebrr has made a chart, here's what they look like: