I agree with above as well as in:
warm - thick/fullier/meatier "fun" sound
cold - thin/edgy/sharp analytical sound
For me too cold or laid-back sound is rather boring to listen to, I generally prefer warm sound even if I might not hear all details as well as on a highly detailed laid-back/thin sounding headphone. I take back what I said about brightness though, the highs and the tonal balance definitely plays a role in it when I think about it, most headphones that are concidered "warm" sounding usually have a low-end and midrange emphasis and usually neutral to dark sounding highs while cold usually have quite a lot of highs present and necessarily not as full midrange and lowend.
Grado's are a bit special case in this case though they really don't have any exaggerated low-end but definitely are very bright yet people call them warm, hmm I'd rather call them forward sounding myself (forward vs laid-back sounding and warm vs cold, is this right?) would be better to speak about I suppose, I've previously somewhat mixed forward and warm sound a bit myself because often warm sounding headphones happen to be also more "forward" sounding like they'd be very similar but I think I'm starting to see the difference now. So to try and sum it up, is this the right definition of warm, cold, forward and laid-back terms?
Warm: Concerning the tonal balance, lowend, midrange emphasis and neutral to dark sounding highs which leads to a more thick/fullier/meaty or "fun" sound.
Cold: Concerning the tonal balance, highs emphasis and neutral to dark / recessed lowend (doesn't necessarily have to be) and midrange, especially recession in the upper-bass to lower-midrange. Thin/edgy/sharp analytical sound.
Forward: Up-front/in-your-face/powerful/engaging sound. Often results in smaller soundstage and more smeared instrument separation (instruments flows into each other creating a more united sound).
Laid-back: Relaxed/distant sound. Often results in bigger soundstage and clearer instrument separation.
Would this be correct to you?