“The process is reversible by washing off any remaining dye. The dye that has diffused into the skin is metabolized and excreted through urine.”
https://news.utdallas.edu/science-technology/yellow-dye-solution-transparent-skin-2024/
The article actually links to an NSF page with instructions on how to perform the experiment yourself:
https://nsf-gov-resources.nsf.gov/files/USNSF-YellowNumber5_Activity.pdf
The paper published in Science:
Achieving optical transparency in live animals with absorbing molecules | Science