Opendesktop.org logo colours. No. 1: Orange folders and yellow active titlebar. No. 2: Yellow folders and orange active titlebar.
In Plasma 5.24 install Lightly from https://github.com/Luwx/Lightly .
In Plasma 5.25 in order to have blurred Titlebar install Lightly from https://github.com/boehs/Lightly .
Choose Transparent Dolphin view in Appearance/Application Style/Lightly/Settings/Frames tab and adjust Sidebar transparency in Transparency tab.
Remember also to choose Lightly in Window Decorations!