Many times contrast is used in logos in order to attract attention for a company. Contrast is especially important because when logos are designed they are constantly resized to fit many different criteria, whether it is a sign, or letterhead, the use of contrast is highly important to companies. Many companies have used this to their advantage by designing simple shaped logos where very little explanation or words are needed to represent a company. For example the logo above expresses a great use of contrast. The simple colors of black and white, along with the unique shape of the symbols used for the logo help to create a simple and clean logo that is a perfect explanation of what the company specializes in, wine. In addition, through the contrast of colors, and shapes, the bottle and wine glass can be easily seen and cleverly expressed.
The above logo for the 2012 London Olympics is a bad use of contrast. First of all there is very little contrast of shapes and becomes hard to read and understand. Even though the shapes create interesting negative spaces, the overall orientation of shapes and sizes are so similar that it is difficult for the eyes to process and visualize. Furthermore, the color contrast is very stressful on the eyes. Although you have two colors, they do not contrast well with each other because the two colors are very intense and bright. This is a bad example because i believe that great logo designs are clever, easy to understand and visually stimulating, not stressful. Furthermore, the text, and the official Olympic logo, along with the logo itself clash because you have rectilinear shapes, and round shapes, and you have text that is neither. Everything about this logo is so confusing that there need to be some sort of correlation between anything.