The Nigerian-born striker joined the Reds in 2007 and has made 82 first-team appearances for the club.
But new manager Mark Robins has deemed Odejayi, who had a loan spell at Scunthorpe last season, surplus to requirements at Oakwell.
Boothroyd has stepped in and agreed a three-month deal for the targetman.
Robins told Barnsley's official website: "Kayode needs to kick-start his career. He will go to Colchester for an initial three months and we will take it from there."