you've received a lot of advice, and i havent read it all, so I apologize if this is repetitive.
First, for a small, initial shirt order, white ink on black shirt is always the safe move. Everyone buys black band shirts, not everyone will buy colored or white band shirts. you dont want to be sitting on unsold merch (ask me how i know)
Second, your guitarists way of communicating is really impolite and not unprofessional. I would address it with him ASAP. Calmly let him know that future critique and comments need to A. Come in a timely manner and B. In a more polite and professional manner. If he can't deal with that, says "poor you" or makes some reference to your derriere and pain, your future as a band is limited anyway. Mutual respect and common courtesy is essential for a band to grow and thrive. As soon as you start making an exception for that one egotistical prick, it will go to hell, if not soon, than eventually.
Third, I think your design is fine. If i liked your band, I would buy it (on black) but, next time, hire someone to do your art. Original art for shirts is not expensive, generally, and the computer generated graphic style can be even less expensive. This way you and your band can all agree on an artist and there is no personal involvement. Trust me, the cost is worth taking yourself out of the role of artist, and the pressure and criticism and blame that can be associated with that... your art is playing bass.