As far as everyday bags I tend to buy more black, that way if I don't have time, I don't have to worry about my bags matching what I'm wearing. I wear almost all black all the time, including my casual and dress clothes, so black bags always work for me.
If it's a bag that I don't really see myself using for work, then I buy it in whatever color I like or jumps out at me, such as green, pink, silver, red, etc. Then if I find a work outfit that matches one of those bags I will carry that bag with that outfit to work. (I hope that last part made sense).