Created attachment 126110 [details]
Preview text files example

SUMMARY
This behavior is also noticeable on some previous versions of Dolphin/KDE.

Preview text files display white text on white icon files, therefore making the preview unreadable.

See attached picture.


STEPS TO REPRODUCE
1. Enable TEXT FILES in PREVIEW tab of GENERAL section of Dolphin's CONFIGURE menu
2. Apply a color scheme with white text or change your current color scheme to use white text
2. Restart Dolphin or in some cases log-out and log back in to make sure
3. Preview text from text files, with and without extensions, .bashrc, .sh, etc.

OBSERVED RESULT
When you choose a color scheme that uses white (or very pale) text and you enable PREVIEW FOR TEXT FILES in Dolphin, what happens is that all text file icons don't show the text preview, because all icons are white and the text is white. Technically the text does display but it's white on white.

If you choose a color scheme with non-white text it will use that color to preview text within the text icon files and then you can read the preview.

However for files with extensions, like .sh as example, the text previews just fine, in BLACK and even with the colors associated to the commands, no matter what color scheme is chosen.


EXPECTED RESULT
If the text file icons are white, then the text should always be black, regardless of the color scheme. In the end, if you choose to preview text files, the text should be able to preview, otherwise it breaks the feature.


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Kubuntu 19.10 - Kubuntu 20.04
(available in About System)
KDE Plasma Version: 5.18.0
KDE Frameworks Version: 5.67.0
Qt Version: 5.12.4

ADDITIONAL INFORMATION