How high does the serum bilirubin have to be before it produces jaundice?

Textbooks say: 50 μmol/L (or 3.0 mg/dL, if those are the units you use).

The first place it shows up is usually the sclerae. Apparently this is due to their high elastin content, though I must admit I have no idea why a high elastin content would make a tissue more likely to bind bilirubin in the first place!

The next best shot at seeing jaundice is to look under a patient's tongue. If the serum bilirubin rises even further, fair-skinned individuals will start to look distinctly sallow...