/etc/fonts/conf.d/10-sub-pixel-rgb-for-kde.conf seems to be included with the fontconfig package. It doesn't appear to be in /usr/share/conf.avail, where I would expect and symlinked into conf.d.
ontop of that, it causes font rasterizing problems in some applications such as GTK applications on KDE where the display is not using an rbg subpixel geometry.

Users should add this to their local fontconfig and probably shouldn't be the default.

Reproducible: Always

Steps to Reproduce:
1. Use the KDE desktop
2. Launch evolution and attempt to read email
Actual Results:  
Text has extreme rainbow fringing

Expected Results:  
for rgb subpixel rendering to be disabled.

I already have an existing $XDG_CONFIG_HOME/fontconfig/ and it looks like KDE's settings application fiddles with it, which may explain why I experienced this issue specifically, despite turning it off there. Either way, the way this file is installed seems wrong to me given most files in this directory are symlinked.

the, workaround/potential fix, is trivial, simply delete the file from conf.d and the problem appears to go away.

Also:
 * I have an existing installation of GNOME and installed kde using @kde-desktop group.
 * # dnf whatprovides /etc/fonts/conf.d/10-sub-pix
el-rgb-for-kde.conf
Last metadata expiration check: 1:06:37 ago on Mon 05 Jun 2023 01:39:47 PM EDT.
fontconfig-2.14.2-1.fc38.i686 : Font configuration and
                              : customization library
Repo        : @System
Matched from:
Filename    : /etc/fonts/conf.d/10-sub-pixel-rgb-for-kde.conf

fontconfig-2.14.2-1.fc38.i686 : Font configuration and
                              : customization library
Repo        : fedora
Matched from:
Filename    : /etc/fonts/conf.d/10-sub-pixel-rgb-for-kde.conf

fontconfig-2.14.2-1.fc38.x86_64 : Font configuration and
                                : customization library
Repo        : @System
Matched from:
Filename    : /etc/fonts/conf.d/10-sub-pixel-rgb-for-kde.conf

fontconfig-2.14.2-1.fc38.x86_64 : Font configuration and
                                : customization library
Repo        : fedora
Matched from:
Filename    : /etc/fonts/conf.d/10-sub-pixel-rgb-for-kde.conf