I'll laugh at this and say that the odds of this happening is pretty rare. I do not own a Chromebook so tragically I can't calculate the exact probability, but my Mac has the same thing. I change it to a color every 5 seconds :)
SO I SET MY WALLPAPER ON RANDOM SO THE COLOR CHANGES EVERY 24 HOURS, IT STAYED THE SAME COLOR FOR A WEEK, I GUESS IT'S TRYING TO SAY THAT I LIKE PINK, LITTLE DOES IT KNOW I LIKE PURPLE. SO EVERY WEEK WHEN IT LANDS ON PINK I JUST HIT RANDOM AGAIN AND CONTINUE MY DAY. YOU MIGHT NOT LAUGH AT THIS