The Hybrid theme for Nikola is a member of the Hyde theme family. You are able to set any subtheme it provides which are the main colours from the base16 project.

I'm not really a fan of these so I added some additional strong colours to the Hybrid theme that I use. My PR to the themes' repository was accepted so this is included in the theme when downloading from the application.

Now there are plenty of subthemes to choose from:

THEME_CONFIG = {
    DEFAULT_LANG: {
        # "hyde_subtheme": "theme-custom",
        # "hyde_subtheme": "theme-hybrid-01", # petrol
        # "hyde_subtheme": "theme-hybrid-02", # dark red
        # "hyde_subtheme": "theme-hybrid-03", # forest
        # "hyde_subtheme": "theme-hybrid-04", # eggplant
        # "hyde_subtheme": "theme-hybrid-05", # dark orange
        # "hyde_subtheme": "theme-base-08", # red
        # "hyde_subtheme": "theme-base-09", # orange
        # "hyde_subtheme": "theme-base-0a", # yellow
        # "hyde_subtheme": "theme-base-0b", # green
        # "hyde_subtheme": "theme-base-0c", # cyan
        # "hyde_subtheme": "theme-base-0d", # blue
        # "hyde_subtheme": "theme-base-0e", # magenta
        # "hyde_subtheme": "theme-base-0f", # brown
        # ...
    }
}

Hyde colours

theme-base-08	theme-base-09
theme-base-0a	theme-base-0b
theme-base-0c	theme-base-0d
theme-base-0e	theme-base-0f

Hybrid colours

theme-hybrid-01	theme-hybrid-02
theme-hybrid-03	theme-hybrid-04
theme-hybrid-05	theme-custom

/* custom subtheme for hyde/hybrid theme */
.theme-custom .hsidebar {
  background-color: #070512;
}
.theme-custom .content a,
.theme-custom .related-posts li a:hover {
  color: #1582ae;
}