All that can make a difference.
Withhold tax depends on:
a) Marital status: married or single?
b) Number of children: more children = lower tax. No children, higher tax.
c)Canton of residence (not gemeinde) = withheld income tax is split among local , cantonal and federal. I cannot find a better source now, but taxes depend on the place you live https://interaktiv.tagesanzeiger.ch/…euerbelastung/
d) Religion declared: if during the registration process at your new residence you declared either Roman Catholic, Protestant or any other flavor of Christianity, you pay religion tax
e) Income level: last but not least, higher salary means higher income. From the numbers, it could be said that your colleague has a lower salary.
But, do your own quality control. HR are only humans, thus fallible. This is the tax calculator:
https://www.estv.admin.ch/estv/en/ho…itzerland.html
PS. I have no interest in your personal situation, so don’t reply with the info. Just input this data in the tax calculator and verify yourself.