Is it permissible not to greet some colleagues in a mixed-gender workplace to avoid their misunderstanding and negative interpretation?

A woman's greeting men with salaam is permissible as long as there is no fear of temptation. You have done well by refraining from greeting them for the aforementioned reason. It is not permissible for a woman to work in a place where she mixes unlawfully with men, except out of necessity.