The flashing and steady signals and colours have the same basic meaning on the ground as they do in the air:
Steady Green (on the ground or in the air) : You are okay to land (air) or take off (ground)
Steady Red (on the ground or in the air) : You are not okay to land (air) or move (ground), so go-around(air) or stop (ground).
Flashing Green : you are okay to join the circuit (air) or taxi (ground), but wait for a steady green before you land (air) or take-off (ground)
Flashing Red (on the ground or in the air) : leave the airfield (air) leave the runway (ground)
Flashing White : come back!