Are tubes really “warm”?

*are tubes warm?*, 
 depends on make of amp/design. in general , no , not muddy (=warm). 
but most ~~certainly~~ not sterile sounding,  that is not clinical as their nemesis, the *other* amp design,
(hint = ss amperage)
yeah i am  #1 basher. of ss design. 
The ss groupies just hate me so...

Summarizing the responses thus far:
Tube fans believe that, relative to ss, tube electronics have naturalness of timber, fullness and air.
Haven’t heard from those who favor ss. I’m guessing that they believe tube “warmth” is a lack of musical dynamics and punch - although I, myself, have not found that to be the case with tubes.
I think we should retire the term “warm” altogether, except to denote preponderance of bass relative to treble, which either tube or ss electronics may exhibit. The stereotypical “Tube sound is warm” seems incorrect.

Usually yes but the degree to which varies widely. 

It depends on the design and the company ARC not to warm CJ warmer etc.

What I really found out in tube amps is you can never get great sound of Strat with solid state amps. The sound won't be warm at all.