Ian Henderson headed the Us in front after quarter of an hour, reacting quickest to Steven Gillespie's mishit shot, but the Bees earned a share of the spoils when Sam Saunders curled home a free-kick 74 minutes in.
Colchester goalkeeper Ben Williams thwarted the hosts on a number of occasions, including quickfire saves to deny Myles Weston and Karleigh Osborne.
Forster said: "They got a lucky break with the goal and I don't think we started particularly well but for the next 70 minutes I thought we played some really good football with good movement and some great delivery.
"If we had been a little bit more clinical in the box I think we would almost certainly have gone on to win quite comfortably. As it was their keeper has also made a series of really good saves which have kept us out.
"We created chance after chance after chance and we moved the ball really well in difficult conditions but in the end it was a great free-kick from Sam Saunders which has kept us in it and given us something to chase."