PHP/Bootstrap grid layout using Ultimatum Theme on Wordpress site

General information for the website: Design website showcasing work
Kind of development: Customization of existing website
Description of requirements/features: Need help sorting out a tricky layout on an existing Wordpress site. See the attached design, it must match this EXACTLY!

Row 1 needs to be full width showing the latest image from the post category.
Row 2 needs to be 50% 50%, showing the 2nd & 3d posts.
Row 3 and subsequent rows should be 33% 33% 33% showing the 3rd, 4th, 5th etc posts. Please note on this 3rd row and subsequent rows the background colour of the block area (shown grey in the attached) must be a different colour based on an ACF colour picker field the user selects when adding the post. The colour picker is already implemented.

We're using the Ultimatum Theme framework, so usual Wordpress theme files ARE NOT used, please do not waste time saying you can do this without checking into the Ultimatum Theme first! I imagine using the Ultimatum Loop system will allow PHP to be used to created the layout.

Any questions please ask, login access available to the site to try it out before you give a proposal.

Thanks
Extra notes: