I saw that and wondered about it. I have read that the F-22's stealth coating or RAM has been problematic and very difficult and expensive to maintain, due to its tendency to degrade. I've seen pics of F-22's with it flaking off, which would have to compromise its stealth. So I would imagine there has been much work to find something that is an improvement. So I'm guessing it is one of 2 things:
1. A new stealth RAM or finish that is very different, and likely more durable.
or
2. It is different altogether in that it is made to be more effective against IR detection, which may be where potential adversaries may have been looking to as an alternative to radar detection. (I've read some speculation that this is it.)
or
3. They simply stripped off the problematic RAM off a few airframes and have been flying them around before applying a new coating.
Maybe there are other possibilities?
I'm going with number 3 just because it is so varied all over the airframe. Stealth coatings, paint, or RAM, in the past, have been pretty uniform over airframes. This looks like it isn't a coating, but rather a strip job down to the bare surface. It reminds me of the F-15 Streak Eagle that set a bunch of time to climb records. It was stripped of its paint to save weight, if I recall correctly.
It will be interesting to see if more jets are sighted with this finish, especially in forward deployments. Or, if we might see F-35's start popping up like this.
Fascinating stuff!