How can I invite my colleagues to the religion and make them love it, despite my shyness and their accusing me of being complex?

Your eagerness to invite your colleagues to the religion is a good thing for which you will be rewarded. Do not give Satan any room to divert you from inviting to Allah, for it is the most honorable profession, as Allah Almighty said: "And who is better in speech than one who invites to Allah and does righteousness and says, 'Indeed, I am of the Muslims.'" You can acquire the da'wah (invitational) style through practice and reading books on da'wah, such as "Islamic Education in School, Home, and Society" by Abd al-Rahman al-Nahlaoui, and "Principles of Da'wah" by Abd al-Kareem Zaidan. For "Indeed, knowledge is acquired through learning, and forbearance is acquired through forbearance." With sincerity, diligence, and asking Allah for success, your shyness will disappear. Be sure to mix with your colleagues in good deeds, for the believer who mixes with people and patiently endures their harm has a greater reward than one who does not mix with them.