Grace making huge advencements in the Eridian medical field.
Turns out there's a childhood disease to the tune of measles that erodes the carapace, and the first symptom shows up about a week before any actual damage is caused.
Grace comments to Rocky that one of his students seems to be turning oxidisation-green. About a week later that student has to be hospitalised for this illness.
Eridian scientists realise pretty quick that Grace can detect the illness long before any of their equipment can, and when caught that early it is much, much easier and safer to treat.
Not only is Grace celebrated in the scientific field for his knowledge and for his part in saving the world, he becomes a beacon of hope for doctors and parents and children on Erid.
The first early diagnosis test involve the equivent of sending a polaroid of the kids to Dr. Grace, who can write "OKAY" or "GREEN" on it
Quickly after that, rocky's color gun can be found in basically any school or clinic. Turns out in the time they've been coming back home, they've accidentally invented a tool that can eradicate the disease
Except Rocky's gun isn't a color gun, exactly, it's a light gun, taking old Eridian camera-tech (likely developed for very niche scientific purposes, to study phenomena in Erid's upper atmosphere or in orbit) and modifying it for hand-held use. If I recall correctly, it wouldn't function in the pitch-dark that is Erid's typical environment, so the medical device that gets created to test for this disease would be Rocky's gun plus a little flashlight attached.
In the future, Eridian children would get regularly checked out with that device to confirm that their carapace reflects only the expected amount of "middle-rough" light frequency. Passing those checks is a prerequisite for the child to go to classes, etc.
And so eventually, the phrase "given the green light" becomes an idiom for "given the go-ahead" on two different planets, for two very different reasons.
















