Kibana 4.1 introduced the concept of field formatters, which allow users to visually transform data fields without altering the underlying data. This feature is particularly useful for displaying information in a more comprehensible way, and the blog post provides a detailed guide on creating a custom field formatter. The process involves understanding the field formatter API, creating a basic formatter to highlight occurrences of the word "error" by either wrapping it in a mark element or converting it to uppercase, and registering it in the application. The formatter is further enhanced to allow pattern-based highlighting by using regular expressions, enabling users to define custom patterns in an editor interface. Additionally, the post discusses the importance of security measures like escaping values to prevent cross-site scripting attacks and mentions future plans to simplify the registration process by providing this functionality as a plugin. Kibana's field formatter API is designed to be flexible, permitting users to extend its capabilities with custom solutions tailored to their specific needs.