helm-themes loads the themes present in
custom-load-themes which are coming from custom-theme-load-path (as per C-h f helps)
After installing themes mega-pack, the list is the following :
Available Custom Themes:
[ ] spacemacs-dark -- Spacemacs theme, the dark version
[X] spacemacs-light -- Spacemacs theme, the light version
[ ] adwaita -- Face colors similar to the default theme of Gnome 3 (Adwaita).
[ ] deeper-blue -- Face colors using a deep blue background.
[ ] dichromacy -- Face colors suitable for red/green color-blind users.
[ ] leuven -- Face colors with a light background.
[ ] light-blue -- Face colors utilizing a light blue background.
[ ] manoj-dark -- Very high contrast faces with a black background.
[ ] misterioso -- Predominantly blue/cyan faces on a dark cyan background.
[ ] tango-dark -- Face colors using the Tango palette (dark background).
[ ] tango -- Face colors using the Tango palette (light background).
[ ] tsdh-dark -- A dark theme used and created by Tassilo Horn.
[ ] tsdh-light -- A light Emacs theme.
[ ] wheatgrass -- High-contrast green/blue/brown faces on a black background.
[ ] whiteboard -- Face colors similar to markers on a whiteboard.
[ ] wombat -- Medium-contrast faces with a dark gray background.
How is it possible to have access to all the other themes available here http://themegallery.robdor.com/
Are they not in the mega pack ?
