To earn the "Casual Speed Demon" trophy in Pic-a-Pix Color, you must complete any 10x10 grid puzzle (Puzzles 6-50) in less than a minute. The timer is in the top right corner.
This is more manageable through normal play than "Tiny Speed Demon", but if you're struggling to work that quickly you can just follow any of the 10x10 solutions in the below Google Drive folder I'm putting together. This will eventually contain every puzzle solution. Fill everything out in less than a minute to unlock the trophy.
https://drive.google.com/open?id=1GouHjmn9DNF034KII1A96lGLKD...