A transparent red dye, 'cochineal red'
can be applied to negatives to lighten areas on the print.
The book "Lootens on Photographic Enlarging and Print Quality" devotes an entire chapter to the method. He refers to the dye as 'New Coccine'. Having read the book when I was ten years old I thought to try the stuff - at dinner I announced that I needed some cocaine, and did they think I could get this cocaine at the drugstore.
I recommend Lootens' book, it is out of print but is available at any used bookstore worth it's stuff will have a copy, prices start at $1.25. A good net source is abebooks.com. I think even amazon.com lists used copies.
The dye is commonly used as food coloring:
I beleive 'Dyene Red Negative Retoucher' is the same stuff, though I have no proof that it is.
And advantage of doing tone adjustment this way is that one doesn't have to go through a big dodge & burn dance for every print. Or to have to try and do the same dance a year later...