Defenders Dean Richards and Ledley King are back from injury for tonight's FA Premier Reserve League encounter against Portsmouth at Havant & Waterlooville FC.
Neil Sullivan and Chris Perry also play but otherwise it's a team of players aged 20 and under and it's those players - particularly the young midfield trio of John Jackson, Mark Hughes and Lee Barnett - that Colin is making his point to.
He said: "I'm sure the lads coming back are looking forward to a game to get a step nearer first team action and the rest of the boys have to do themselves justice to keep their place.
"They have to grab the opportunity. The young centre-backs have to be patient at the moment because we've defenders coming back and they need to play.
"That will change throughout the season. It will be forwards, midfield players - so they have to grasp their chance and take it.
"Darren Anderton, Kazu Toda and Jon Blondel will all look to be coming back soon so those young midfielders have to do it now. If there is one spot up for grabs when the senior boys come back, they have to be the one to take it.
"That makes it more competitive for us and when the senior lads come back, it will be tough to get into the side.
"So players will be judged during the week in training and they will keep their place in the team if they do well - that's where I want to be this season.
"They have to train well, perform well, their attitude has to be spot on and if anyone dips out, they will lose their place. That's a great incentive to keep everyone eager."
The reserves drew 1-1 at Leicester City last week in the FAPRL South opener. In the rest of the section draws were again the order of the week, with only last season's champions Watford recording a win at Nottingham Forest.
Last night, Charlton beat Wimbledon 4-1, with Chelsea overcoming Arsenal 3-2 and West Ham and Derby sharing the spoils in a goalless draw.
Colin Calderwood has told his young guns to grasp their chance now as senior players start to return to reserve action.