Top Law Schools

I have letters of rec from 3 of my college professors. I have been working for about 1 year. Should I get a letter from a colleague/ boss and substitute one of my college ones with it?

You can if you think you have an employer who would write a really good letter for you. But outside of Northwestern (which I think requires one letter to be from a job), there's no need. Most adcomms indicate that they prefer academic LORs anyway.