If interested purple is 380nm. Olympus uses a UV2A coating which starts at 380. Panasonic uses a UVA coating which start at 450. This is on the sensor filter which is why Panasonic (some, not all) lenses can have purple flare and fringing on an Olympus camera. And of course they no longer sell 2A filters so I cannot replace my 15/1.7 since I sold it with the filter.
Diffraction at this time is a physical property of light passing through an opening which applies to cameras and telescopes. There is always some diffraction. Whether it can be detected depends on the device detecting it. If the device is an m43 20mp sensor, it can be detected at f/8. This means when cropping a lot of printing large. For normal uses, it is not visible. At F11, it can be seen in 11X14 prints and on video displays sometimes. If the sensor were a 40mp sensor the individual pixel size would be 1.4 smaller. This would allow diffraction to be detected at f/5.6 and and visible at f/8.