Possibly. There isn’t—as in the app itself—a Tinderbox method for that but AppleScript could probably set an RTF string with coloured $Text. Whether that can be persisted back in to Tinderbox you’ll just need to try.
You could insert HTML markers into $Text, which would show in Preview and get exported.
Unless the words are unique, like a product name, be careful with a regex-based approach. They match characters not semantics/contexts, and many words have different meanings according to context.
To understand better, what is the use case (the need) to do this? I ony ask in case that suggests an alternative approach.