It's a common example of how regional dialects can change the pronunciation and spelling of words. While standard English uses "yellow," the Southern dialect often uses "yaller."
Here are some examples of how it's used:
* "My dog has a yaller collar."
* "That tree has yaller leaves."
* "She's wearing a yaller dress."
While "yaller" is considered a dialectal term, it's often used in literature and media depicting Southern characters or settings to add authenticity and flavor.