I had some red gel which I cut to shape and put a couple of layers in behind the glass of my AA sized Maglite (With LED lamp replacement) It works really well too but same problem, it is only handy if you already have the gel otherwise it can be a bit costly depending on if you can get it in a small amount.
If I go to a star party I cut a bit of gel out and stick it to the front of my iphone to make it usable at night without doing dark adaptation in. I should remember to tape over the camera flash too, just in case.
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