That typically can be a hard question when trying to pick out clothes for yourself, you and your spouse, your children, and or your family. Don't spend the long hours trying on clothes in the mirror or buying clothes but you still don't feel confident in it. Once you find the right attire that works for you, you know that you have found the right clothes. Think about dressing it up and making a more elegant look for your session. You have to be confident and claim that outfit and wear it with true pride.
I always strive on having my clients wearing neutral colors for their sessions. If a clients wants a certain color, maybe help guide them to go a little darker than on the brighter side. For example, if the client wants to wear Red, suggests like a burgundy or maroon color. If they want yellow, suggest a mustard yellow. For green, try a olive green, if they want orange then try a burnt orange or copper color. Navy blue is a good recommendation as well when taking pictures. I wouldn't go with a light pink, but more like pale pink color. Also, please stray away from neon colors, it doesn't add great features to the pictures like the neutral colors would.
As a photographer, it's okay to help guide your clients on what certain colors to go for because of lighting but also to make sure they look the best in their pictures. Depending on what they are wearing, it's important to make sure the location spot matches their attire as well.