Passage: The design of the flag was originally conceived by NASA planetary scientist Pascal Lee during the 1998 Haughton-Mars Project arctic expedition to Devon Island, Canada. In addition to symbolizing liberty as a tricolour flag, the design evokes a vision of the "future history" of Mars in which the planet is transformed from red, to green, and then blue like the Earth. The red bar, which lies closest to the mast, symbolizes Mars as it is today. The green and blue symbolize stages in the possible terraforming of Mars, should humanity ever have the ability and will to undertake such a task; the ethics of terraforming remaining a matter of debate. Kim Stanley Robinson's popular science-fiction trilogy Red Mars, Green Mars, and Blue Mars also provided inspiration for the flag. Beyond any human-induced terraforming, the color sequence also depicts the environmental change Mars might experience on astronomical timescales as the Sun evolves into a red giant and Mars becomes warmer. In the Pantone Color Matching System (PCMS), the red is the "Red Clay" (18-1454), the green is the "Mint Green" (17-6333), and the blue is the "Imperial Blue" (19-4245).

Question: Use of the color red is meant to stand for what planet?
Mars