The w3-hover-border-color classes change an existing border's color when you move the pointer over the element.
Move the pointer over each box to see its border color change.
Each box uses w3-border for a border on all sides and w3-leftbar for a thicker left border that makes the color easier to see.
The gray and grey spellings produce the same colors.
w3-hover-border-amber
w3-hover-border-aqua
w3-hover-border-black
w3-hover-border-blue
w3-hover-border-blue-gray
w3-hover-border-blue-grey
w3-hover-border-brown
w3-hover-border-cyan
w3-hover-border-dark-gray
w3-hover-border-dark-grey
w3-hover-border-deep-orange
w3-hover-border-deep-purple
w3-hover-border-gray
w3-hover-border-green
w3-hover-border-grey
w3-hover-border-indigo
w3-hover-border-khaki
w3-hover-border-light-blue
w3-hover-border-light-gray
w3-hover-border-light-green
w3-hover-border-light-grey
w3-hover-border-lime
w3-hover-border-orange
w3-hover-border-pale-blue
w3-hover-border-pale-green
w3-hover-border-pale-red
w3-hover-border-pale-yellow
w3-hover-border-pink
w3-hover-border-purple
w3-hover-border-red
w3-hover-border-sand
w3-hover-border-teal
w3-hover-border-white
w3-hover-border-yellow