I was at Neuchwanstein today (I'll upload a pic or two later)...
Expect the colours to peek during the next week or so, if they do turn properly.
Overnight, last night, there was snow down as low as Fussen. The problem here is that cold weather will burn the leaves (they'll turn brown, not yellow/orange/red.)
If you are looking to get a photo of the front of the castle with the hills behind then you at least need to be an expert bush walker and/or mountaineer...
The way up to the places that deliver that view are not easily reached - I broke two walking poles today attempting to do so. In many places, I was on all fours trying to ascend or descend and the walking poles were a burden. Going for the occasional slide on one's ass was required. There are no paths to follow, no signs or markings to show you the way. You must discover it for yourself. I cannot recommend anyone trying to do it now that the ground is wet and slippery (in some places I was walking through snow.) If you think that you're capable, do it in summer (July?), just to get to know it when the ground isn't slippery and come back for the autumn shot. Difficulty out of 10 - 9.
There is a trail from Marienbruch to Tegelberg, but that will not get you *that shot*. Even then to get an unobstructed view of the front of the castle requires leaving the trail and entering dangerous ground. If you're afraid of heights or not steady on your feet, forget it.
I'll summarise - do not go to Neuchwanstein and think that you can get the "fall colours" shot of the castle with the front of it and the hills behind if you've never shot that angle before.