To earn the "Tiny Speed Demon" trophy in Pic-a-Pix Color, you simply need to finish any of the first five puzzles with a 5x5 grid within 15 seconds. It'll probably take you memorising the layout of a previously completed puzzle to get it rather than using the usual deductive reasoning (unless your brain works particularly quickly).
Luckily you can find all of the 5x5 solutions in the below Google Drive folder. (Eventually this will contain every puzzle in the game). Load up one of the first five solutions, commit to memory, and colour the squares correctly as fast as you can. You'll unlock the trophy if the timer in the top right is less than 15 seconds when you complete the level.
https://drive.google.com/open?id=1GouHjmn9DNF034KII1A96lGLKD...