Here is a fix for Clemetine, also mentioned in this bug report:
# This is for the mono themes, change it to suit your needs
#THEME="light"
THEME="dark"
mkdir -p "$HOME/.config/Clementine/customiconset/icons/22x22"
mkdir -p "$HOME/.config/Clementine/customiconset/icons/32x32"
mkdir -p "$HOME/.config/Clementine/customiconset/icons/48x48"
ln -sf "/usr/share/icons/ubuntu-mono-$THEME/apps/24/clementine-panel-grey.png" "$HOME/.config/Clementine/customiconset/icons/22x22/clementine-panel-grey.png"
ln -sf "/usr/share/icons/ubuntu-mono-$THEME/apps/24/clementine-panel.png" "$HOME/.config/Clementine/customiconset/icons/22x22/clementine-panel.png"
ln -sf "/usr/share/icons/ubuntu-mono-$THEME/apps/24/clementine-panel-grey.png" "$HOME/.config/Clementine/customiconset/icons/32x32/clementine-panel-grey.png"
ln -sf "/usr/share/icons/ubuntu-mono-$THEME/apps/24/clementine-panel.png" "$HOME/.config/Clementine/customiconset/icons/32x32/clementine-panel.png"
ln -sf "/usr/share/icons/ubuntu-mono-$THEME/apps/24/clementine-panel-grey.png" "$HOME/.config/Clementine/customiconset/icons/48x48/clementine-panel-grey.png"
ln -sf "/usr/share/icons/ubuntu-mono-$THEME/apps/24/clementine-panel.png" "$HOME/.config/Clementine/customiconset/icons/48x48/clementine-panel.png"