Manager Geraint Williams introduced Richards as a 62nd minute substitute for a tiring Matthew Mills, who had made a good debut at the heart of defence since his loan move from Manchester City.
But Richards took his chance with both hands, scoring what proved to be the only goal of the game just four minutes later.
The ex-youth teamer rose high to head home Kevin Watson's excellent corner as Colchester chalked up their 12th win from their last 13 home fixtures. In fact, the Essex club have not lost at Layer Road since they were beaten in their first two home matches of the season way back in August.
This latest success was no more than Colchester deserved, especially as they had to cope with the absence of their star player Greg Halford, who had completed his £2.5million move to Premiership side Reading just a few hours before kick-off.
John White, another product of Colchester's youth team, came in and did a good job at right-back in place of Halford, and the U's generally coped well without their star performer of recent seasons.
They created by far the better chances all evening with midfielder Kemal Izzet going close with a couple of shots from long range.
Johnnie Jackson was also thwarted by Preston keeper Andy Lonergan, as well as having a couple of other efforts charged down by defenders. For Preston, David Nugent had very few glimpses of goal, although he was narrowly off target with an angled drive on 27 minutes.
Midfielder Paul McKenna squandered their best chance to grab a point when blasting over the top following Nugent's excellent cross, but Colchester were not to be denied and have now taken 37 points from a possible 39 in the last 13 matches at home.