I know that the colors aren't the best, but you can see the problem: those red squares form ALMOST a pattern. Not enough to complete a pattern, but almost... Even if you put them in 3 of the 4 corners or any other way I've tried to fix the problem.
Now, 2 squares of the same color are easy:
Four are obvious, they can go on one of the diagonals (or in the corners, but I didn't illustrate that.)
This one is 6, AND 5, so you can see that while there are a bunch of two colors, neither overwhelms. Your eyes see PATTERNS!
This one is 6 of one color, the rest are a mix. Still, your eyes see patterns and are happy. See what I mean?
Okay, it was pointed out that it will sometimes work this way (but only if the colors play well together!)