I have a non-profit client that this opening a kind of "branch" organization. The second organization will have it's own site with it's own URL, but they would like to keep the same theme for both sites, but with a different color scheme. 

There will be shared content on both sites, but most pages will be at least a little different. The "About" page will be similar, but on the new site, there will be information about the original organization AND information specific to the new "branch."

My initial gut instinct was to port the Domain Acess module for this project. BUT, the more I think about it, Domain Access might not be a good option if the content is similar but not the same. Both sites will have a page at /about, but the content will not be exactly the same and the paths will conflict. I don't think Domain Acess is good in this scenario. Domain access would be great if pages with the same path had the exact same content.

I've never really used Multi-Site before, but maybe it's the better solution here. Although, I'm not sure if it's that much better than just building two independent sites. 

What advice do folks have?

NOTE:
Domain access is a suite of modules for Drupal that allows one to build multiple sites using a single database and share content amoungst the different sites. It has not yet been ported to Backdrop CMS, but there has been strong interest in completing that port. 

Most helpful answers

SSO was provided by another company, the module that is used on D7 is OpenID Connect (openid_connect) with OAuth authentication and Real Name module.  

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I still think Domain Access, once ported, would have value even where content is not shared if users were shared.

I also think, once ported, it will make multiple site management for the same owner simpler than multisite

Multisite could work well depending on your workflow, but it can be tricky to setup automated workflow.  In this scenario, they would probably have nearly all the code in the shared module and theme folders and just the content and config would be separate, but you would also need separate users.

If you have your workflow already geared for single site then having a separate site may be your best option currently if you can't wait for domain access.

I had very bad experience with Domain Access for only two sites.  It was more efficient to sync content via feeds module (as long as one site is designated as primary) and keep SSO so users can have same login for both sites.  

SSO was provided by another company, the module that is used on D7 is OpenID Connect (openid_connect) with OAuth authentication and Real Name module.  

The opening question:

a kind of "branch" organization. The second organization will have it's own site with it's own URL, but they would like to keep the same theme for both sites, but with a different color scheme. 

This might also be done with Organic Groups where each branch is a group. Additional benefits include that important pages can exist as a single page and add each branch that needs access to it. Likewise, roles like editors at different branches might be given permissions to update the pages used by multiple branches.

The url redirection and display may need some attention.

The solution depends on the workflow desired.

 

@izmeez For this project, I should have been more specific, each site will be need to be at it's own domain, not just it's own URL. 

I don't think I can acheive different domains and different themes with Organic Groups, or?

(Actually, the theme thing could probably work, but I'm not sure about the domain issue.)