Sometimes balls change colors due to age or horomonal issues, could be a type of minor scarring - sometimes simple things like a difficult shed or rubbing up against something in the cage can cause these. Could also be the start of an IMG color change their brown starts to lighten as well as the increase in black. Really hard to tell - as long as it doesn't appear to be sensitive and the scales look clean and bacteria/fungus free I wouldn't worry about it too much. Keep an eye on her and see what happens.
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Tosha 
"Nihil facimus sed id bene facimus"

10.35.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Anakin Skywalker)
0.0.1 Green Tree Python (Verdi - yeah I know but my kids love the book)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Desert Tortoise (Pope John Paul aka JP )
2.2.1 Fish (1,2,3,4)
0.0.1 Lizard rescued from feline
0.0.0 frogs rescued from pool skimmer