Boss Bar

The BossBar is being used to display the progress of a raid. It has been implemented for all the versions.
1.7 requires BossBarAPI or BarAPI plugin
1.8 requires BossBarAPI or BarAPI plugin
1.9 uses CraftBukkit's CraftBossBar so you don't need to use any other plugins.

As you probably know, 1.9 has customizable bar style and color.

And this is default config which is described in config.yml

bossbar:
 enabled: true
 raidbar:
  enabled: true
  style: SOLID
  color: PURPLE

Available styles:

SOLID
SEGMENTED_6
SEGMENTED_10
SEGMENTED_12
SEGMENTED_20

Available colors:

PINK
BLUE
RED
GREEN
YELLOW
PURPLE
WHITE