Hi @rinkusamanta12. There aren't any native color options in the Rich Text editor, but you can use Rich Text Labels to create span elements with aa given class so that you can add your own custom CSS to the selected text.
Here's another thread that discusses this:
And here is the article where you can learn more about Rich Text Labels:
https://intercom.help/prismicio/en/articles/1943308-add-custom-styles-to-rich-text