(sigh)
Adrenaline is not stored per character, but PER SKILL.
http://gw.gamewikis.org/wiki/Adrenaline
Have you noticed that when you strike you lose adrenaline in all the skills?
Adrenaline works that way to prevent adrenaline skill to be used without any kind of delay.
Adding that option would require to change ALL the adrenaline skills so they have increased 'casting' or recharge delays.
Adrenaline skills are not spamable, and they are meant this way.
And, more important, HP is RED, XP is GREEN, Energy is BLUE.
You have there RGB, so... there are no color left for another bar, sorry.