Any oil-based finish will darken your wood up just a bit. That will include varnishes, as they are generally oil-based. On a lighter wood like maple, it won't darken it up very much at all, and may add just a tint of a yellowish color to it. Quite pleasant, if you ask me.

If you have enough for a test sample (even a small one), it would be worth putting just a bit on it to see exactly how much it will darken.

If you don't want it to darken up at all, you'd have to either stick with no finish (maybe just a good waxing, which really would be a nice finish, to be honest with you) or use a water-based finish.

If you have access to a Woodcraft (or similar woodworking store), look for General's HP water-based finish or Deft water-based clear finish - both are a bit pricey, though. You could probably find a water-based finish at Lowe's or HD, too.