What is this part? (H2D)

Hi Folks,

A little orange/red-ish film fell from my toolhead while I was doing maintenance today [H2D]. Looking at some photos online, I’m quite sure it’s this guy in the photo below (circled in green). I’m wondering if someone could help me with:

  1. What is the name of the part this film is attached to?

  2. What is it for? I.e., should I replace the part just because the light-filter (which I think it is) fell off? – I’m also wondering if I can just glue this thing back. Looking at the part that fell, it seems it was attached with some kind of thich adhesive (resembles B-7000 people use to close phone cases)

Thanks in advance!