Colour

Claude Monet - http://www.aliexpress.com/item-img/Monet-Field-of-Poppies-II-famous-hand-made-Oil-Paintings-Reproduction-On-Canvas-Landscape-handpaint-oil/563645092.html

Here is an image thats using colour to create space; having the red flower in the foreground brings them to the front, as our eyes automatically put this colour first its not necassarly because it's bright a bright colour. Then to have the background a blue colour what's a a lot cooler colour, gives it so a further a field is present in the image giving it a sense of distance.