iPad apps gone dark mode

I'm delighted that you have self-identified and corrected the problem.

For the benefit of other readers who may encounter a similar problem - if the screen colours consistently appear to be distorted or unnatural, you need to check some key Accessibility settings that are intended to compensate for specific colour-vision issues:

Settings > Accessibility > Display & Text Size

Ensure that all settings enclosed within the red box above are switched OFF/Disabled.

If your iPad is running iPadOS 26.x, from a Home Screen, touch-and-hold any empty area of the screen. When the screen icons start to wobble, tap the Edit button seen at top-left of the iPad screen; this will open a menu.

From the menu, select Customise - this will open a new window at the bottom of the screen where you can customise various aspects of the screen appearance:

With the exception of the Customise title, every element within this window is a functional button - that changes an aspect of the window appearance. The brightness/contrast button is perhaps more subtle in its effect - noting that this button has two settings, this being indicated by an equally subtle appearance of the associated icon. The effect of other buttons should be immediately apparent upon experimentation.

Selecting the Default button and setting the brightness/contrast button as shown here might reset the appearance to your accustomed settings