The moves were made before Saturday's game against Cleveland.
Colon batted .302 in 19 games with the Royals. Nix was claimed off waivers Thursday from Pittsburgh and arrived in time for Saturday's game.
The 32-year-old Nix hit .111 in 16 games with the Pirates. He began the season with Philadelphia.
Colon, who started seven games at second base and three at third, was the fourth overall pick in the 2010 draft out of Cal State Fullerton. Kansas City plans to recall him Tuesday after Northwest Arkansas' season ends and major league rosters can be expanded to 40.