If you have some application that doesn't respond to touch event (let's call it 'sensitive app'), potentially you have malicious application.
To find potentially problematic\/malicious applications do the following:
1. find red marked application in list (red marked applications are currently running),
2. open the application details (click on the application),
3. choose 'Force Stop',
4. return to the 'Obscure Window Detector' application,
5. check if application is still red, if not, try to open 'sensitive app',
6. if application is still red, try to uninstall it, and then try to open 'sensitive app'.
7. touch the '>> TEST HERE <<' to check whether you have just stopped the problematic application, if the field becomes GREEN, you found the right one, if the field becomes RED, you need to repeat the procedure from the beginning.