plank-themer
http://rhoconlinux.github.io/plank-themer/

elementary-tweaks
https://www.unixmen.com/customizing-plank-elementary-os-luna/

elementary-plank-themes

themes
/usr/share/plank-themes/

https://aur.archlinux.org/packages/?O=0&SeB=nd&K=plank-theme&outdated=&SB=n&SO=a&PP=50&do_Search=Go
https://www.pling.com/browse?cat=273

https://github.com/erikdubois/plankthemes
https://www.linuxnov.com/top-10-plank-dock-themes/
https://www.deviantart.com/customization/skins/linuxutil/applications/docks/whats-hot/?qh=&section=&q=plank&offset=0
TransPanel
    https://github.com/rhoconlinux/plank-themer/tree/master/themes-proposed/Elementary_Update/TransPanel
    https://github.com/arcolinux/arcolinux-plank-themes/tree/master/themes/TransPanel
mac
    https://www.gnome-look.org/p/1201564/
    https://www.gnome-look.org/p/1215851/
    https://www.gnome-look.org/p/1208015/
    https://www.gnome-look.org/p/1264834/
mojave
    https://www.gnome-look.org/p/1248226/
        https://aur.archlinux.org/packages/la-capitaine-icon-theme/
        https://www.addictivetips.com/ubuntu-linux-tips/install-mac-like-la-capitaine-icon-theme-linux/
frost
    https://www.gnome-look.org/p/1111286/
    https://github.com/dikiaap/frost-plank-theme
    https://snwh.org/moka 
        community/moka-icon-theme
foggy
    https://www.gnome-look.org/p/1201603/
        cupertino icon theme
            ? aur/faenza-cupertino-icon-theme
            ? community/mediterraneannight-theme
                xfwm4/unity/gtk2
        https://www.gnome-look.org/p/1102582
wingy2r
    https://www.gnome-look.org/p/1192956/
docky
    https://www.gnome-look.org/p/1161721/