KDE is an international technology team creating user-friendly free and open source software for desktop and portable computing. KDE’s software runs on GNU/Linux, BSD and other operating systems, including Windows.
If you encounter a bug, proceed to https://bugs.kde.org/, check whether it has been reported.
If it hasn't, report it yourself.
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Thats determined by the profile your konsole is running. As you cant change the default, duplicate it, set it as your new default and then change the colors of it.
There is also one of these tempting "Get new" buttons there, if you wanna look for profiles online... Be careful tho, many people have spend many hours on customisation after they clicked that button once
Like the other guy said, the appearance of the actual terminal is determined by the profile, and the applied color scheme.
The color scheme of Konsole is part of the profile. To create a new one: Right click anywhere>Menu>Settings>Configure Konsole
Click profiles, in the top right click "New".
Click Appearance. From here you can add, change, and edit the available color schemes. Once you're happy, click Apply. Close the dialogue.
Select the new profile and make it the default. Done.