The colors of the jacket pattern and the pocket square pattern are too similar in value (both are light grey tones) . There needs to be more contrast between the two. To me this doesn't work. I would substitute a white linen in that plaid jacket and never give it a second thought.
lol, that picture was mine. It's actually very desaturated. The pocket square is this one:
and looks more vivid IRL. The jacket is grey and I often do wear a white linen with it .