Try gaffer tape instead. It blocks all the light. It doesn’t reflect much light at all. It generally sticks to anything. You can get it in a variety of colors. It doesn’t leave as much sticky residue when removed or repositioned. I’ve not encountered many surfaces (expect painted surfaces) that it actually damages when carefully removed. I use black gaffer tape on basically all my electronic stuff: one strip to cover the whole light, two strips a razor’s edge width apart so that I can still see the indicator if I try but otherwise 99.9% of the light is blocked, or a strip with a folded over tab at one end for the displays I want to block %100 of the light %90 of the time.

Duct tape, duck tape, electrical tape, masking tape all really suck unless you love that sticky gunky residue they inevitably leave on everything. Gaffer tape isn’t perfect, but it’s much better for this kind of semi-temporary light blocking without too much surface damage kind of job.