That's pretty much any finish that cures/hardens. But only lacquer and water-bourne finishes will minimally alter the native colour of the wood. The lightest shade of shellac (bleached) might also suit if you were okay with applying it to such large surfaces.
As Andy mentions do expect the wood to change colour over time, chiefly from light exposure. In effect the bed will get a suntan
I was shown some photos the other day of when this couple had their pine staircase put in about 25 years ago with an oil-based varnish on it, at the time it looked quite nice, whilst it was a little more orange than unfinished wood it wasn't overly orange. Fast forward 25 years of sunlight the thing is practically the same colour as someone with a bad fake suntan who may be a world leader.
So in all, whatever you put on it will affect the colour somewhat, but not as much as UV will in a few years time.
And oxidation. Almost everyone seems to forget that exposure to air itself contributes to colour change in wood. Even film forming finishes don't prevent molecular migration of air into and out of wood, with the possible exception of epoxy resin type finishes, and I don't think even that finish is a complete barrier to molecular transfer from one side of the film to the other. I could be wrong about that though. Slainte.