Avidyne IFD550 Pilot's Manual page 74

IFD500 Series Pilot Guide
Any obstacle in the database within a 5nm radius of the aircraft
position and whose top is within 2000' vertically (above or below)
of the aircraft altitude will generate a cyan (blue) threat bubble
over the obstacle on the SynVis scene.
Blue Obstacle Threat Bubbles
Obstacles inside a 3nm radius of the aircraft position and whose
top is between 100' below aircraft altitude and 1000' below
aircraft altitude will generate a yellow threat bubble over the
obstacle on the SynVis scene and the map pages.
Obstacles inside a 1.5nm radius of the aircraft position and
whose top is between 100' below aircraft to anything above
aircraft altitude will generate a red threat bubble over the obstacle
on the SynVis scene and the map pages.
2-8 SVS Subsystem