红色的 (hóng sè de) is an adjective meaning 'red' — literally 'red color's', where 红 means 'red', 色 means 'color', and 的 is a grammatical particle that turns the noun phrase 红色 into an attributive adjective. Unlike English, Chinese adjectives often require 的 when modifying nouns, especially in descriptive or formal contexts. It’s used to describe anything with a red hue: objects, clothing, animals, food, or abstract concepts like 'red light' or 'red flag'.

This form is neutral in register and common in both spoken and written Mandarin. While 红 alone can sometimes function adjectivally (e.g., 红苹果), adding 色的 makes the description more explicit and natural in standard usage — particularly when emphasizing color as a defining trait. It’s frequently heard in daily life, from describing fruits and traffic signals to cultural symbols like red envelopes or red pandas.