Complementary colours are those which sit opposite each other on the colour wheel. Each one is actually made up of each of the primary colours - red sits opposite green which is made from blue and yellow; yellow sits opposite purple which is made from blue and red and blue sits opposite orange which is made from red and yellow.
When placed next to each other, these colours make the other appear brighter and more vibrant. This means you have to be careful how you use them, but they are certainly useful when you want to make something stand out as they create a strong contrast.
Sue Tonga has chosen a complementary colour scheme of red and green, using papers and embellishments from the gorgeous MME Lost and Found 2 Rosy collection. By using faded reds as the dominant colour, splashes of green as a colour pop and neutrals of black and cream to soften, Sue has achieved a balanced colour scheme that doesn't detract from her photos.
Complementary colours provide a nice contrast that is pleasing to the eye but it is important to use one colour as the dominant colour and the other in a supporting role. By using different shades of the colours, you can achieve a visually interesting colour scheme.
Suz Doyle has created this layout as a record of the issues her poor old son has with sleeping. She made good use of the darkness around the edges of her photo and printed her journalling directly onto it.
In this layout Suz has used fairly equal amounts of the complementary pairing of orange and blue, and it works because they are used on the neutral base of the cream cardstock and mostly black photograph. Despite searching through her piles of papers and finding a multitude of orange and blue alternatives, she ended up using no patterned paper as the strong colour combination seemed to keep dominating the page. She opted for a lighter smattering of SEI buttons and gorgeous Webster’s Netting to give the colour pop without overwhelming the photo.