How about:
Color Your World Challenge
MOC display showing how color influences the world. Must FEATURE the Original LEGO colors. Red, Yellow, Blue, White and Transparent. Other colors can be used but these must be prominent in the build.
Size – no bigger than a 32×32 baseplate wide – so multiples can be used in display case.
“When Lego started manufacturing bricks, it started small, colorwise. “These were very basic colors,” said Signe Weise, a corporate historian at Lego. The original brick colors, according to Weise, were red, yellow, blue, white and transparent.”