To earn the "Casual Smarty Pants" trophy in Pic-a-Pix Color, you must complete any 10x10 grid puzzle (Puzzles 6-50) without using an X. This means you can't mark any of the blank squares with an X using
, you must just commit the white spaces to memory or work around them.
Alternatively you can just follow any of the 10x10 solutions in the below Google Drive folder I'm putting together, which will eventually contain every puzzle solution. Just follow the picture filling in only the coloured squares and the trophy should unlock.
https://drive.google.com/open?id=1GouHjmn9DNF034KII1A96lGLKD...