My glasses are strong enough and with high enough refractive index that if I look at a point light source through the edge of a lens I can see a rough spectrum of it. I can easily tell a true violet LED from red+blue or yellow from red+green. Used to be able to tell white LEDs from incandescent but the LEDs got much better.

Take a photo of them. Then zoom in. If that doesn’t blow their minds, take a video of them and play it back.

Digital cameras have been commercially available as early as the late 80s, but were of course super low res and with terrible image quality even accounting for that compared to what I just carry in my pocket now.