I think the OP's statement & query is completely valid. A Dolnet may not be 'dark' in comparison to a Conn or Holton, but in comparison to a Yama or Yani, Cannonball, Antigua, etc (you get my drift)....it sure is.
Compared to most contemporary models, it is quite Dark.
So...yes, Conn is considered dark and I agree...using a definition of the quality of the harmonics which are prevalent in the horn's intrinsic sound (yes, every model has an intrinsic tone due to its specs). I also use the quality of the 'spread' of the tone, to a degree....as often harmonic boost and harmonic spread go hand in hand....
Personally I consider Conn, Holton, B&S, and Keilwerths to be the kings of darkness. But it can certainly be said that Martin, King, Buescher, Beaugnier, and some of the Italians to a degree are also 'dark' horns. Again, especially compared to modern horns, most vintage horns blow darker. This doesn't mean they are NOT flexible enough to sound bright and edgy...because all of them can with the right setup and player. But again, their intrinsic qualities lean towards 'darkness' in tone.
(Inevitably someone is gonna come along with the "it's 80% the player & mouthpiece setup, notsomuch the horn" line or such and such, if they haven't already...which is an oft-heard but pretty specious opinion which too often has been spread and taken as fact - and as a quick example of how this can be contradicted one need only simply have a look at one of the YT 'sax showdown' vids made by sax.co.uk - where the player and mouthpiece setup and room and recording device remain completely consistent, only the horns being blown are different....thus illustrating that the significant differences in tonal characteristics one is hearing (bright, dark, focused, spread, fat, thin, vibrant, dead, edgy, smooth, smoky, reedy, etc.) are in fact the result of the particular piece of hardware (aka the sax) being played. I sorta hope this thread doesn't digress too much into that 'debate', for the sake of the OP especially, who again asked a valid Q, IMHO).
So, to the OP, there's MY list:
add to it some others
Then I throw in, as far as contemporary horns: