Is it supposed to change for existing installs? Mine did not change. Not complaining I prefer no accents. Fresh install on my laptop has it tho.
Plasma theming is... special. Enable menu / panel transparency and you'll change theme 800x for it to actually apply your setting, then it randomly drops it like it has again for me.
EDIT:
Typical, switch to light theme and back again and now I have the accent colours. 👍️
EDIT2:
Got transparency back, but when you have a window maximised on that screen transparency goes away