We buy almost all our kids' clothes secondhand. One lesson I've had to learn time and time again is NEVER TO BUY NAVY! Not Old Navy, but the color navy. The cotton turtleneck will never match the knit pants, which are a completely different shade altogether from the winter coat. Why is there so much dye variation with navy? Even if you manage to make a successful combination, the navy will, over time, look more tired than any of the other clothes in the closet. My only exception is for fleece items and the occasional handknit sweater--but only because they will be paired with khaki bottoms.
Another tip: whenever possible, buy dark shoes instead of light. They show much less wear. I found these Stride Right wides for $1, and they go with almost every outfit. Why? Because he doesn't wear navy pants.
Above: Andrew's outfit, head to toe, cost less than $5: off-white Gap turtleneck, Kite Strings fleece vest, Osh Kosh corduroys, and the aforementioned shoes.