What to wear for a family portrait, I think, is the most stressful question of a photo shoot. Everyone wants to look their best, but without compromising their individual sense of style, both as an individual and as a group. I have compiled a photo diary of what I like and don't like, both for color and style.
Don't like:
One color for everyone. This falls into the good and bad category. Sometimes it can make a crisp, clean photo, which can be appealing to the and other times it just looks like a sea of color with floating heads.
Sea of White - very popular in the late '90s and early '00s. Part of the reason I don't like the sea of white is because it is way over done, everyone is doing it. I think most people do it for the simplicity, especially in large groups. But I like color and something as simple as a red scarf can add interest and fun to an otherwise boring photo.
Black. My issues with all black: it makes an otherwise bright photo look dark, all black on white people equals for pasty skin tones, it doesn't transfer well to black and white - it results in a floating head.
http://www.flickr.com/groups/1321846@N23/
http://www.striking-photography.com/2010/11/family-studio-portrait-photographer-longmont-boulder/
Other colors
Color, yes. But it's hard to see where one person ends and the other begins.

http://dallasheadshotphotographers.com/2010/10/dallas-family-portrait-photographer.html
Jewel tones (red, green, purple, blue), I think, are especially difficult to do all one color. One of the major issues with jewel tones is that there are various hues of the same color. I see two major problems with this, one it can end up looking like a bruise or just odd. In the photo below the theme was red but because dad's shirt is a slightly different shade of red it makes him look like the odd ball.
http://www.studiotampa.com/tampa-family-portraits-in-the-park/
More jewel tones. Just not a big fan of the purple/blue combination.
http://www.photosbykoos.com/family.htm
Too much color. When there are a lot of colors in the clothing it makes the photo look busy with no focal point. You don't know where to look.
http://www.robison-vattuone.com/?p=167
No neutral base color. I can almost hear the conversation (I know because I've had it) - Person in charge of photo shoot, "We'll all where yellow, pink, or green," certain family members, "but I don't own anything in pink, yellow, or green and I'm not about to go out and buy something I'll only where for the photo shoot," person in charge, "fine, where black or whatever." The color combination isn't bad but makes for a busy photo. Again, the eye doesn't know where to look. It's nice to have common color to create cohesion, but it's best to make the common color(s) neutral such as grey, beige, or black and to add pops of color with an open jacket or sweater or a scarf.
Likes:
I really like this photo both for style and color. There is a cohesive color theme of neutral black, gray, and blue, but it keeps from being mundane due to the pops of color of pink, brown, and white. Every one is dressed according to his/her style which makes the photo look easy and relaxed.
http://aniafieldsphotoart.com/blog/?tag=sauk-prairie-wi-family-portraits
I like the color palette. The colors are complementary (red and green) with the third being a nice neutral. I like the bold colors.
http://www.powhatanphotography.com/Powhatan_Family_Portraits.html
I really like the colors and style in this photo. It's one of those photos I look at and at first I think, "Why do I like that? None of the colors go together, there are several different patterns. But I love it." Then upon further study I begin to see the cohesiveness and the thought that went in to make this look work. First, color. The palette is yellow, orange, black and white. Yellow is in the girl's dress and the mother's cardigan. The orange is found in the dad's shirt and the girl's dress. The black and white is seen throughout in the mother's dress, the girl's stockings, and the other girl's jacket. Finally, pattern is considered throughout. The dad and the son, although wearing different color shirts, are wearing similar check patterned shirts. The mom and the daughter add a bit of quirkiness with the patterned shirt and stockings and the other daughter's ruffled dress ties her into the quirkiness.
Perhaps I have over-analyzed it. But hey, I design clothes and it's the details and how they work together that impress me the most.
http://simplicityphotography.com/blog/?p=2575