website with different nav menus & colour schemes



I am about to start work on a website. The company has 3 different divisions, therefore I will have a landing page where the visitor can chose which of the 3 areas they can go into.
For the 3 divisions, I basically want them to all have the same layout but i’d like them to have different main navigational menus to each other. E.g. division 1 may have 10 pages but they will all have the same main navigation. Division 2 will have X pages and they will all have a different main navigation.

I may also want each division have a slightly different accent colour.

What is the best way of doing this please? 3 separate wordpress installs?, or is there a plugin that could manage this?
I haven’t yet decided on a final theme for this (so any suggestions on one that would be best for this appreciated). I am currently playing around with Enfold.

I am just getting back into Wordpress after about a year off, so there may well be a simple solution that I am just not seeing.

Many Thanks