Were the original episodes in black and white? If so, when did the first colorized episode air?

The first color episode was the first episode of the second season, Gilligan's Mother-in-Law (I think that's the name of it)

Yes that's right. I was just watching it. Also, there are some strange things about it in the credits that happen only in this episode. There are two:

1) The ship in the background while they show he cast members in the steering wheel is different from the one seen in the rest of the color seasons.

2) Dawn Welles is shown before Russel Johnson on the screen.