I could be wrong here... But I have just painted my zed and I know exactly what your talking about!
The dull patches are bits which need to be compounded out. This can be done by hand or machine.
If the paint is older than 1 month you can use T-cut, if not use some 3m compound.
Apply the compound and rub in a circle motion then use some soapy car water and wash it off. Easy!
Also, It is recommended to leave the paint alone for about 2-3 weeks clean, so no wax or polish, but compounding is fine, as the paint needs to harden properly.