Be sure that you have finished the decoding the picture label at bottom left f the lock-pick book. That is the clue.
Then do the file cabinet puzzle.
The lock pick first inserted is the one at bottom right, going clockwise.
The lockpicks: yellow at bottom right; red at bottom left, blue at top left and green at top right.
The "every second one" code stated by the book is: R - Y - B - G - G - G - B - R - Y - R - B. These are the colors.