When you work with custom CSS classes in combination with other frameworks, it's perhaps a good idea to prefix your own classes, for example project:text-mycolor instead of just text-mycolor.
No matter which other framework you are using ... here Filament also uses TailwindCSS with its own classes. If you want to use YOUR own classes, you need to define different classes than those one used by Filament. To ensure you are the only to define your own classes, you can prefix them.