Why Isn't There More Research on This?

Maybe there is, but I'm not having much luck finding it. . . it's come to my attention that sometimes my classroom teacher friends are questioned on "letting students color." How it's "a time filler" and "maybe not the best use of students time."  Some Google searching on my part gave me some articles, but not what I was looking for: academic articles with data, real research and hard numbers.  Not exactly art integration, but information on what coloring, cutting & gluing do for academic achievement and overall student performance.  While I'm not a fan of coloring sheets, I do see value in students creating, coloring and cutting/gluing.
The Crayola rep that served our area (for years and years) retired, and I don't know her replacement's name, so I don't have Barb to email.  I sent out some feelers to the university that sends me student teachers, but they're doing finals (maybe already on break?) so no response yet.  
Not just to help out teacher friends, I'm really curious to see the numbers on this.  Anyone have any scholarly article links you could point me to?
Thanks art teacher internet friends, and hold on, winter break is just around the corner!