In a brown study
Definition 1 of 1
Pro Tip 1/3Not Literal
The phrase isn't about color or studying, but implies being lost in thoughts. 
During the meeting, I glanced over to see Jenna in a brown study.
Pro Tip 2/3Archaic Usage
It's old-fashioned; use it to sound poetic or in historical contexts. 
The character from the Victorian novel remained in a brown study throughout the scene.
Pro Tip 3/3Emotional Nuance
Often implies a hint of melancholy or preoccupation when deep in thought. 
After hearing the news, he was left in a brown study, contemplating what was to come.