Different colours have different meanings:
- Blue: the line is controlled by your side with map points controlled or contested by your faction at both ends.
- Grey: the line is neutral, controlled by no side either due to assault teams having not yet passed along it (common early in the game) or due to a skirmish taking place along the line.
- Red: the line is controlled by the enemy with map points controlled or contested by the enemy faction at both ends.
Note: Colours above are for the Friend or Foe map colour scheme. For the Strategic map colour scheme, Blue would become the colour of your faction and red would be the colour of either of the enemy factions. For example if you are US, Blue becomes Green and Red becomes Red and Purple. For guidance on switching colours see here - Map Overview > Purple Box.