In this UN billboard, we notice the use of typography and color to communicate the message ("translating war into peace"). Even if the invisible typography clearly specifies the message, it is actually the last thing we read in the poster. In fact, we are first attracted by the A in red. Then, we notice the bird flying in white. The white and blue contrast makes us want to understand what surrounds the bird. Finally, we understand that it picked the A from "war" to place it in "peace". 

This is an excellent combination of typography and color with a strong message behind it.