I did some testing, and I can confirm that three white "bolts" in the alertness level will NOT count as 'detected'.
My testing methodology and results:
I re-played "The Loyalists" mission (which is very fast to finish, if you already know what's going to happen), and made sure I finished the game with 'Ghost (Never Detected)' checked in the mission stats. I then loaded an earlier save just before putting the final moves that will finish the mission, and then fired a crossbow while not sneaking near a bunch of guards and tallboys which alerted most of them to at least three white "bolts"/levels:
I immediately hid back to avoid getting a 'red' alertness level, and then proceeded to finish the mission. Missions stats say that I still got 'Ghost' checked. I therefore conclude that getting all three white alert levels (but not reach red) will not count as detected.
Also, from this post in the Bethesda forums by Gstaff, a Community Manager at Bethesda. (i.e. legit):
How do the detection markers work that appear over NPC (non-playable character) heads?
There are four levels of detection.
Level 1- One marker will appear on either side of the NPC – The NPC has caught a glimpse of your character or heard a non-threatening sound.
The NPC will not actively search.
The NPC will return to patrolling or idle after a few seconds without further alerts.
Level 2 - Two markers will appear on either side of the NPC – The NPC has seen your character or heard a threatening sound.
The NPC will actively search for a several seconds and up to a minute.
The NPC will return to level 1 after a about a minute or two without further alerts.
Level 3 – Three markers will appear on either side of the NPC, and they have not turned red. In this case, the NPC is very close to finding or being aware of your character’s presence.
The NPC will actively search, up to several minutes.
The NPC will return to level 2 after about a minute without further alerts.
Level 4 – Three markers will appear on either side of the NPC, and they turned red - The NPC has spotted your character and is actively engaging him.
The NPC will enter into combat and actively chase / attack.
This level will count as an official sighting of your character and will count against stealth-based achievements/trophies (i.e. Ghost, Specter).
If the NPC loses sight of your character, they will search for several seconds.
The NPC will return to level 2 after a few minutes without further alerts.