The colour of a cover will not tell you anything about the IR properties you are looking for.
There are black covers which allow IR transmission and you can find clear covers which will block IR transmission.
What you have to look for is:
- wavelength of your LED
- transmission of that wavelength of the cover you want to use
Now, you can hope that they have not modified the transmission of acrylic outside of the visible spectrum while tinting it green and use a sample of a PMMA transmission curve, which will look something like this:
As you can see it has a wide transmission range from 350 nm to 1600 nm - which should cover your IR LED (usually around 950 nm).
The green will have an effect in the range from 390 nm to 700 nm (visible spectrum) but not necessarily in the IR range.
For example there is this:
Which starts to transmit really only after 800 nm, which means it is black (maybe you can see it as very dark red in bright enough light) but IR will still pass through.
And when guessing the question remains, is it even acrylic to begin with or did they just label it that way...