Colored projects on a planning report

What if you want to create a planning report where the projects have different colors like this:



And not like this:    or  

Keep in mind that table cells are formatted from left to right, first the cell on the left, then the one on the right.

First step is to remove the black cell border on the right side of each cell:

Then create a conditional formatting rule to add a matching color cell border on the left side: