OnePager allows you to automatically change the color, shape, or other formatting of task bars and milestones based on the data in your project plan. For example, you could specify that every task less than 10% complete be colored red. This is called conditional formatting, and basically it works the same way as it does in Microsoft Excel.
To set a conditional formatting rule, go to Home > Project View Properties > Task Bars and click on the Manage Rules button at the bottom:
An editor will pop up, and you can add any logical rule you want by clicking on the Add Rule button. In this example, we'll set the rule we suggested above - that every task less than 10% complete be colored red:
Click OK twice, and you'll see the rule take effect.
The conditional formatting rule we've set will now be applied to our project view, including for every new snapshot we create. So if a task changes from 5% complete in one snapshot to 15% complete in another snapshot, its color will change in the second snapshot from red to whatever color it would otherwise be assigned.