May be asking for trouble getting into 'is it really their favorite' in another thread. Its a bit up in the air if any of this is true, for never sure anyone actually asked a royal, or making assumptions on what color they seem to like more often who knows but:
Elizabeth is said to love blue
Revealed: Why blue is the Queen's favourite colour... and why she doesn't like beige | Daily Mail Online
But like the comments on Diana, seem based on what color she wears most.
Princess Charlotte's (little surprise for a girl her age) has been confirmed pink.
Princess Charlotte's Favorite Color Is Pink | PEOPLE.com
Kate has said that she doesn't have a favorite color, but if she had to choose it would be white?
Things You Never Knew About Kate Middleton - Kate Middleton Facts
9. She wears lots of colors, but really likes white.
Kate claims she doesn't really have a favorite color — but if she had to decide, it would be white.
William seems to have revealed on a talk show some of his favorites
While on BBC Children's program he did say he preferred Blue, he gave his list of favorite things.
Favorite Food Banana Flan
Favorite Movie Italian Job
Favorite Novel Fledgling Jason Steed
Favorite TV show Top Gear
Favorite Color Blue
Favorite Soccer team Aston Villa
Harry is said to love orange. But considering the article claims it is because of his hair, taken with a cruise ship full of salt.