5mth old glows yellow when tired or crying

I have a foster daughter with a baby girl born in June. She did not need to go under lights and was not considered jaundice.
The last few weeks whenever she gets tired or cries she glows yellow like a glow worm. It fades away as she settles down and she is normal baby colour most of the time.
Dr has ordered a blood test although my DFD (dear foster daughter) does not know what test it is but I would imagine it would be FBC and LFT.
She has not been told what he is looking for and I have tried a google but all it brings up is baby jaundice.
Any ideas ?

My dad has Gilberts Syndrome. He goes yellow when he is tired etc. Is basically jaundice for grown ups I think.
I guess seeing as your DFD's daughter is still a baby, then she is having trouble breaking down the bilirubin, just like newborns who are jaundice.
It's more common in breastfed babies I believe.
But good that the dr is doing tests to rule out other liver problems.

well so far all her tests have come back normal although she now has bronchiolitis and an area of infection in one lung.