How to format resource utilisation?

I have a spread sheet that has is for resource utilization on projects.

It has a column for projects, employee names associated to the projects and start/end dates.

The goal is to show if people have been allocated to a project at all times and try not to overlap.

So far I've marked the weeks where people are on projects as green using conditional formatting. However how can i mark the weeks where the the person is not on a project as red?

I've created 2 spreadsheets which I think are good and interactive but It's hard to fit what I'm thinking in.

Anyone have ideas?

Thanks in advance

one way would be to select the range, and change the colour of all the cells to red, then let conditional formatting change to other colours when conditions are met.

another way may be to do =NOT(green_formula), and then positioning it in the list to suit your company.

these options depend on what you consider to be "not on a project", because there are 7 days in a week and you havent said what happens when their dates fall within the middle of a week.. are they on or off?