Gantt Chart - Changing Cell Color Based On % Completed

I'm trying to create a simplified Gantt chart of sorts, and cannot figure out one piece of it. I'm not sure how to write out exactly what I need, but here goes.

I would like to have a formula that looks at the percent completed (which the user inputs) and multiplies it by the total duration for the task to give a total number of days completed. Then, under the corresponding dates, the color of the cell would change. I've attached a simplified version of what I'm talking about.

On the attached spreadsheet, the total duration (D2) is 5 days and the percent completed (C2) is 40%. This calculates to 2 days. With that said, I would like the cells under the first 2 days under the listed dates (E2 and F2) to change color. When the percentage complete reaches 60%, then G2 would change color, when it reaches 80%, then H2 would change, and when it reaches 100%, then I2 would change.

My guess is that the formula will need to result in a particular value, and then I'll use Conditional Formatting to do the actual changing of the cell color. Assuming this is correct, I still don't know what formula to use to accomplish this.