Planning home improvements necessarily involves addressing numerous practical matters. That doesnt mean you should ignore the fun stuff!
The Fun Stuff
The first thing to plan for in home improvements is the practical stuff. The second thing you need to talk to family members about is the fun stuff.
Most people have colors they like and colors they dont like. They have things that interest them and things that dont. Get your family to talk to you about those things. Each persons bedroom, or bedroom area, should reflect his or her taste and interests.
A boy who likes green, football, and backpacking can easily have a sage green (it reads as more neutral than many shades of green if re-sale of your home is a concern) room with cream woodwork, cream interior shutters, and cream ceiling. Framed football posters and wilderness scenes might be pleasant. Bedding with a rustic motif (rows of stylized pine trees?) from L.L. Bean or Plow and Hearth would work right in. Add a touch or two of a bright color like red or yellow.
Does he need a desk in his room? A chest of drawers? A bookcase? Would he enjoy having a bulletin board? Even if...