The KDE themes aren’t changing right. When I change a theme, it only changes the decorations and the panels and widgets. The rest of the theme remains same.
How can I change the grey area (IDK what its called)?
Its something that's tripped me up a few times - 'themes' in KDE4 seems to refer to the window decorations theme, when it also meant, IIRC the themes used for application in KDE3. There is a way to change this - the colours module, though this is less than apparent
You need to change this in the KDE colours module - simply type in colours in the KDE menu
You can pick a pre-created theme from the scheme tab - this is a useful starting point for customisation
Or Create your own theme in the colours tab if you need to tweak colours -the 'inactive' and 'disabled' tabs that also affect parts of the theme, and options affects where the theme is used (for example in non KDE apps) and other such things