If you have a preamp with tone controls and turned the treble counterclockwise you could hear a warmer sound but most audiophiles know that this extra circuitry will degrade the sound to some degree and there will be some loss of transparency & fine detail, few exceptions do exist. You can still have a combination of warmth, transparency, and fine detail with high quality preamps/power amps without equalization and is accomplished in other ways. A component that sounds bright or warm has little to do with its overall sound quality, matching of components is critical here.
The final sound of any given component of course is engineered into the product by the mfg so that when matched with their line of components the desired outcome is achieved otherwise it is hit or miss. That is precisely why many quality components are designed by ear. When you buy a component you are agreeing that they, the manufacturer knows how to produce a product that sounds good to you whether it sounds bright or warm.
I was told by an electronic tech that he could change the sound of any preamp or power amp by swapping out resistors. Aside from a warm sound & resistors, the sound you hear with any component has just as much to do with other parts and their implementation. Although varying degree of quality in resistors do have a substantial impact on sound.
Some audiophiles prefer a more extended, revealing sound while others prefer a warmer sound. That is exactly why we have an amp/preamp game. I have had a combination of components in my system that produced a warm sound, got tired of that and went back to a more extended, revealing sound.