To temporarily highlight blowout and underexposure in the picture, use View | Show Blowout [Shift+O] or click the icon with the sun symbol in the Histogram section of the side panel.
In regions with blowout, one or all color elements have reached their maximum values. No room to go higher means no room for variation, so regions with blowout lack detail. Overexposure is actually not the only cause of blowout; it also will appear in regions with strong light sources, like the sun or a fire. Blowout does not automatically mean a bad photo, though multiple and large regions with blowout do mean a bad photo. In some places, blowout is inevitable (e.g. reflections off of shiny objects). Blowout highlighting is informational only. It makes no sense to, for example, darken a photo just so that Zoner Photo Studio stops highlighting blowout in it: the detail has already been lost, so darkening won’t restore it.
Zoner Photo Studio can highlight eight different types of blowout: blowout in the R, G, and B channels, combined RG, RB, and GB, RGB (places where all three elements have blowout), and summary blowout, where even though there is no blowout in the individual channels, their sum exceeds a certain threshold. You can choose to have areas without blowout be displayed in grayscale or in color. Areas with blowout are shown in saturated colors representing the affected channels: red for R, green for G, blue for B, yellow for RG, purple for RB, cyan for GB, and bright yellow for RGB. Summary blowout is displayed in medium yellow.
Zoner Photo Studio can also call attention to underexposed areas – overly dark places lacking detail. These places are displayed in bright sky blue.
You can change how blowout is highlighted using Settings | Preferences | Other | Display of blowout and underexposure. For more on this, see the topic about the "Other" section of the program preferences.
Pre-Print Color Preview
The View | Pre-Print Color Preview option [Shift+P] has no effect unless you have turned on color management Settings | Preferences | Color Management | Use color management) and selected a printer profile. This function translates the picture using the color profile that the printer would apply during printing, and displays the result on-screen.
The Show Blowout function and the Pre-Print Color Preview function behave similarly. They only change the way the picture looks on-screen. For all other purposes (e.g. when saving), the program works with the original source picture. Also, these functions turn off automatically when you switch among pictures.