Plagiarism is copying without atribution. There is no plagiarism if the audience knows the source of the text, without the speaker mentioning the source. Recall Abraham Lincoln and the House Divided Speech. The audience (then at least) understood this as a reference to the Bible.
To have a valid trademark, the related consumer must recognize that there is a single source for the marked good or service. Just seeing pink fiberglass indicates a source without stating the source. If one passes off one's good using another's trademark, that is problem. However, if one says my fiberglass is better than pink fiberglass because (...), that's a different story.