Quite pleased: I added native #thinfilminterference in an absorbing layer on top of a conductor to #blender3d. I went through the math of https://hal.science/hal-01518344/document, and added terms dealing with absorption in the film. Slightly trickier than I thought, but it works. The 5.0 alpha branch dealing with dielectrics was great as a starting point!

The render shows the result with nodes on the left and the native implementation on the right. If you look carefully there's a slight color shift.
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#b3d