I was picking out some coloring books for my friends children when she informed me that she would like to get a couple of books too. This is a 30 something year old woman. She then began picking out colored pencils as well with a gleam in her eye like a kid in a candy store. She couldnt wait to get home and start coloring in her new books. She picked Barbie Doll, princess type books and methodically chose what colors she would use for the first picture.
If you really want to get right down to it, adults love to color as much are their kids do. If you dont believe us, think about all of the artists that do oil and watercolor paintings, those that do pen and ink drawings and watercolor pencil drawings and artwork. This is simply the more appropriate and acceptable way for adults to continue coloring as we all did as kids. This is partially why both adults and children alike really enjoy having SpongeBob printable coloring pages available to them to color on.