"Warm" is the most overused word on this forum, bar none. It is used to describe anything with transformers, any type of microphone in existence, or any type of gear that somebody may like. Basically, the only things that are not "warm" are Graham-Patten preamplifiers and A/D converters (the DMIC-20 and the ADC-20). Grace Design stuff is warm, but only in isolation. If you compare any Grace Design preamplifiers to another piece of equipment that is not made by Graham-Patten, the Grace stuff is "detailed" while the other equipment is "warm." If you are describing a Grace preamp, you could say, "man, Trey was really on last night; good thing my V3 has that nice warm sound to bring it out. That guy over there was running a 722; I prefer a more detailed sound. That 722 is just too warm for me!"
If you say something is "bright," fine, it has an accentuated high end. If you say something is "dark," it has an accentuated low end. If you say something is "warm," then it does not have a piece of equipment made by Graham-Patten in the signal chain.