In my experience yes valve amps can indeed sound warm
My 'warm' experiences with valve amps have been with an unmodified pair of Quad II's and with a Chinese Ming Da amp. Other than that the other valve amps I've had do not sound 'warm', just right to me
I will try to list the 'non warm' sounding valve amps I've owned, these are the ones that I can remember
1st was a Decware SE84
2nd was the Rogers E40a
3rd was a Chinese YAQIN MC-100B KT88 (not 'warm' sounding at all, quite 'sharp' and 'brittle' sounding to me)
4th was an Audio Note Conqueror 300b
5th is the Oto SE
6th is the Meishu
Colin has NVA monoblocls and NVA pre and whenever I listen to his system it sounds great, much punchier sounding and the bass it better than my own system but I still prefer my current SET amps sound
I can't imagine that I will ever go back to ss as I have become so accustomed to the sound of my SET amps and find them the most pleasing sounding to me
When I do listen to ss amps they seem to miss the 'character' and 'feeling' of good valve amps however that might be because I haven't listened to the 'right' ss amps
Many many years ago I heard a very expensive system which included some huge Mark Levinson monoblocks and I was completely underwhelmed by the sound and this was probably the most expensive system I have ever heard
However that is just my opinion and my experiences