It's been said that Wally's lightning effect will be white going forward while Barry's will be yellow, to help differentiate them visually.
Okay, but that's confusing considering the hint that Dr Manhattan has white sparking too, and the Watchmen are involved in the mixing of realities here, perhaps indicating Dr Manhattans presence?
In the Flashpoint mini-series, Flash went back in time and accidentally changed the present. In the new present, Bruce had died instead of his parents, and his father had become Batman. So when Thomas Wayne figured out that Flash was going to put things right, he gave Barry a letter to give to Bruce when he got back.
It's a little unclear when, from Barry and Bruce's perspective, the events of Flashpoint happened, but presumably at least right before the events that took place in all of the new52 #1 issues (aside from the ones like Justice League #1 and Action Comics #1, which took place in the past). So that would mean Bruce has had the letter for a couple of years.
Speculation is that Barry remembers the Flashpoint incident, and having met an alternate Thomas Wayne, but he thought he just put everything the way it was. He didn't know that things still didn't actually go back to the way they were before he left.
Also good information, that puts a perspective on the letter I never realised. It was a Batman writing to another Batman, and Thomas Wayne knew Flash was intending to return things to the way they were. But the Flash didn't quite do that. Also strange.
Okay, but that's confusing considering the hint that Dr Manhattan has white sparking too, and the Watchmen are involved in the mixing of realities here, perhaps indicating Dr Manhattans presence?
The lightning associated with the Dr Manhattan scene is blue, all the Flashes in this issue have the same red/yellow lightning. All the lightning has a white centre to create an intensity.