As Terran
Make:
Viking
Ghost
MarauderVikings remove the reason bio cannot stand and fight.
Open in the counter tool with Colossus tagged ->As Protoss
Make:
Tempest
Immortal
DisruptorRange or burst beats Colossus better than matching only gateway units.
Open in the counter tool with Colossus tagged ->As Zerg
Make:
Corruptor
Viper
HydraliskAbduct or Corruptor focus turns Colossus into a liability.
Open in the counter tool with Colossus tagged ->
Zealot
Adept
Stalker
Sentry
Observer
Warp Prism
High Templar
Archon