If you are struggling with what colors and styles to wear for your session, take a few of these things into consideration. 1) what colors/tonality and style is the room you will be displaying your session in? You want to compliment the room. Just as if you were buying a fine art painting, you would select your colors and style of clothing in the same manner. 2) what is "normal" wear for your family? If you are a jeans and trendy top kind of family or if you're an everyday khaki family, you should dress for your session how you are most comfortable. This will allow you to be more relaxed, as well as relieve some pressure from feeling as though you need to "dress the part".
This family is a great example.