Maybe it's to distinguish Nala as a main character, instead of just a brief character that's only on the screen for 5 minutes and never returns again. Sarafina, maybe for genetic reasons or she didn't look right with colored paws. That reason could have went for Nala, too.
Well, they don't have colored paws because Disney wanted them to look really beautiful and feminine. Unlike their muzzles, which are a lighter color than their coat color, Disney wanted Sarafina and Nala to look an actual real-life lioness. That is why their paws aren't colored like the rest of their pride.
I think Nala and Sarafina have plain toes like the rest of their pelt is because the filmmakers wanted them more beautiful and more feminine than the others and more different rather than looking the same like Sarabi and the others, just like their ears that don't have the dark rings on them. when TLK 2 came out they made Kiara more like Simba except for her ears which she got it from Nala.
They probably drew her like that, so people would no she had no relation to Simba or his family because I've heard the rumor of people thinking that Nala is scars daughter which is completely ridiculous!
Reasons why Sarafina has colorless paws.
(1) To distinguish her from the other random lionesses in the movie.
(2) Makes her look more feminine and beautiful.
(3) She probably didn't look right with colored paws.
(4) It's a trait
Reasons why Nala has light colored paws.
(1) To make her look like Sarafina.
(2) It's Genetic
(3) It's a trait
(4) To distinguish her as main character
(5) It makes her look more feminine and beautiful
(6) She probably didn't look right with colored paws either