The concept of the ending is that Shepard after being hit with the beam when assaulting is knocked unconscious is that the rest is in his head..
(I can't recall if you believed that or not).
But basically, it's a Reaper introcdonation in his head, the blue (good) view, is the reaper telling Shepard it's the good view, not that it actually is.
If you recall Anderson AND the Illusive man said the Reapers cannot be controlled, therefore the blue ending is a lie, Shepard dies.
(Notice in the preview the Illusive man being absorbed)
Green ending is kind of a mix, but again Shepard dies. Can't remember much of it.
Red ending is the good ending, but like said, the Reaper is trying to tell you it's the wrong decision, notice he says 'remember you are part synthetic', but doesn't actually say you will die. You've been fighting all this time to kill them, and most people don't pick this ending, because they're being told by a Reaper it's the bad ending.
(Notice Anderson destroying them).
After cutscenes, Shepard is seen in the rubble back on earth, taking a sharp breath from unconsciousses, which also supports it's in his head.
Proofs of this theory here, lots to make you think about it: http://drsteinman.hubpages.com/hub/P...fect-3s-Ending
Which I fully believe..