I'm in marketing, and we are about to beta a desktop application with a black user interface. There are areas that have red text on black, blue text on black, and the menu bars are a dark shade of gray with white text. The new functionality is great, but I'm concerned there could be issues with headaches, eye strain, readability, etc. I need some advice on what types of questions to add to the usability testing document to get impactful information. UI is not my specialty. Thanks.
As with all user experience questions of this sort, the answer to the question lies in looking at who the application is for, and where, how and when it will be used.
Who is it for?
Are you able to characterize the age of the user base? Older users tend to have poorer eyesight. An application targeted at those past middle-age should use forgiving contrast ratios and generous font sizes.
Where will it be used?
Is it the application intended for a particular installation? If it's not intended for a single-space installation, do you anticipate it will typically be used in an office environment with bright flourescent lighting? A design-studio-style space with dimmer or natural light? The more you know about where the application will be deployed, the more you can tailor the brightness and contrast of the application to fit into the ambient light of the space.
When and how will it be used?
Is the application intended to be used for extended periods of time, with someone staring at a terminal screen for hours on end? Is it designed to be glanced at periodically, like a dashboard? Is it meant for use on desktop machines, tablets or large-format displays? Answering these questions can help inform the degree to which you need to consider eye strain and fatigue in your UI design. In general, extreme contrast ratios are better for distance viewing and brief, periodic usage. A hard-white-on-hard-black UI may look slick at first, but after the eighth hour of a workday, the users will be rubbing their eyes before heading home.
Some questions I could think of that would help would be "Could you see yourself comfortably looking at this website for more than thirty minutes?" or something to that effect. The worst thing about high contrast designs is not that they're hard to glance at but that they're hard to stare at.
All that said, if you're asking a panel of people if it's too high contrast, it probably is.