Neutrals
I encourage you to pick clothing that you feel comfortable in, communicates your style and compliments your home decor--and I suggest you go with a neutral palate. Your new baby should baby should be the center of the attention in your session, so dressing in bright colors or busy patterns with draw our eyes elsewhere in the image. Neutrals do not have to be boring all white shirts, they can be gray, navy, tan, white, ivory, soft blue, soft pink, etc. The most important part is that the colors compliment each other, try sticking with 2-3 colors max. Men typically have a hard time finding shirts without pattern, if this is the case I suggest wearing a solid sweater overtop.