Yep, avoiding red eye is obviously the best approach, but I’m processing photos from 20 years ago at the moment, so I’m trying to get the best out of the garbage I have 
I’m going to play with the DeltaE sliders more to see if I can master them. I can dial in a colour, but then it sometimes doesn’t select anything, even though that colour exists in the image. I then start tweaking the sliders until I see the mask take effect, but I’m not sure whether I need to adjust luminance, chromaticity, range, etc. I’m not sure I fully understand the bottom sliders yet. The tooltip says “Weight in the deltaE computation”.
Thanks for the tips!