When you make an artwork which is based on black, white and grey, it's all about brightness, no other dimensions. Shapes and holes, lights and dark.
When you decide that the design will only be white and black, whitout grey, it's not an easy job to do.
But if you put some elements of colors into the design, it changes all relations. Color can sometimes more freely "breath" in composition with less chromatic colors or greys. Besides that, grey sometimes becomes color, as a contrast to a color, which is in compostition with, or which is next to it. There's a large amount of really good black and white designs to find on the internet.
Just a little bit of pink on the exactly right places. Color always come with a shape. Could you find better color instead of pink for this particular design?
Next design is based on the same idea, but as the color has been changed, the shape has to be modified as well. And - in this particular case - bigger number of the green shapes is allowed, probably because of the shape characteristics and non-agressive nature of the color.