Hi @JuanM thanks for posting this question! Glad you're already looking into whether Portals or Embed might be a good fit since it sounds like custom customer-facing branding is important for your use case. You can customize branding (color, favicon, etc.) on both the Business and Enterprise plans. For the floating Retool logo at the bottom left specifically, that can be removed/hidden if you're on the Enterprise plan.
So on either Business or Enterprise you could customize accent/header background colors, the logo for the login screen/top menu bar, favicon etc. in Settings > Branding (see screenshots below - please excuse my made-up branding in my test instance, I'm clearly not a brand designer 
)
Since the floating logo can only be turned off if you're on Enterprise, and my test instance is on the Business plan, it has the "Hide menu" option greyed out (below). If Enterprise might be something you'd explore, I'd recommend booking time to chat through options.
