Probably chroma, like everything else here, then.

[At least that makes sense to him - and makes sense as to why Byleth can still kind of communicate, and kind of make contact, even if he's invisible.

Sure, it makes chroma generation inconvenient at best, but... if some inconvenience is all they have to go through to drag him back to the realm of the... living? Existing? Then it could very much be worse.

The not-quite sensation that he can only assume is from contact with Byleth is still odd, though.]

Yeah, I did. I still can't see you, but I can feel that you're here.