For the contest theme "islands," I created very simple "desert islands" in a rough polka dot:
The colors are the same as from the palette-restricted "sailing" theme. I used some details to try to expand the apparent number of colors: the sand is white speckles on yellow, the water is dark blue crosshatching on light blue, the palm leaves are yellow lines on blue to give a green impression, and the palm trunks are red lines on blue to give a purplish-brown impression. I feel it would work rather well as a Hawaiian-style shirt.
My favorite was this rather glowy overhead map. Mine didn't crack the top half of entries.