Age old battle: programmer vs designer or ponytails vs black socks.
Just adding something to the advice that has already been offered. Is the position/job description/responsibility of you and your boss well defined? Even if you have shares in the company, that does not necessarily mean you can make decisions or offer input in every process of the company.
For example, I have shares in a company that creates cosmetics. I am very opinionated, as I guess you probably are. I would not dare, though, making comments or offering advice about the smell of the new bath products they are launching even if I think they stink (which I don't, they rock), because that is completely out of the scope of my responsibilities. I can have opinions, as every human is entitled to have, but it is not my place, my right or my responsibility to share them or try to enforce them if they are out of my scope.
So, are you just hired to implement what he designs, which in many cases is the case? Or are you supposed to critique his graphic design as well? Be careful if crossing those boundaries, because it creates a muddy slush that very often end ups in war. Nasty one.
Another comment: I can guess that, from the tone of your question, your advice probably does not come as a subtle comment. Mine was like that as well, and I had to learn to tone it down and sweeten it a lot. Like they say: you catch more flies with honey than with vinegar.
(BTW: I personally both have a ponytail and wear black socks)