> There seems to be real dark one and a milky white one.

AFAIK the very dark one is for the wavelength used for IR
remote controls

The milky white I've only seen in PIR apps, which is a much
longer wavelength. The detectors themselves (eg piezos)
aren't sensitive to visible or near-IR frequencies. You may
find that the lens material is the filter rather than the colour

A blank photographic negative is a fairly good (better than
nothing) daylight filter for IR

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