Would you say vocals are very natural sounding or do they come through with some colouration?
I'd say vocals sound natural. Period. Like a person in the room. I would not call it colored, no. It is not warm or glowing...it's just very real/natural sounding (this also assumes an excellent vocal recording). So no, not tube-like, but it somehow seems to give a nod in that direction. It definitely does not sound like a typical classic SS amp like a Krell or Levinson (though they both have made quite a wide range of amps so I am stereotyping - pun really wasn't intended there). The KWA150 does a very good job of getting out of the way. Disclaimers apply.
Add Daedalus to your short list of speakers if you are considering a KWA150 - That pairing is absolutely wonderful. I have no interest at all in Daedalus, nor do I own a pair. I have heard the pairing extensively at Dan's place, both the Ulyses and the DA-RMa. If you have the space and budget the Ulysses is killer - if your space is smaller the DA-RMa gives you the same magic in a smaller package and with less low end grunt (which is prodigious with the Ulysses). I'd certainly also highly recommend AudioMachina, which I do own, but they're at a much higher pricepoint. Great synergy with the KWA. I do some work for Karl, so disclaimer there.