The red wavelengths of light are the longer wavelengths and the violet wavelengths of light are the shorter wavelengths. Between red and violet, there is a continuous range or spectrum of wavelengths.
The USPS also includes that a large postcard is 49 cents to mail. The maximum size for this postcard is 11 1/2 inches long, 6 1/8 inches high and 1/4 inch thick. This is the same rate to mail a First Class 1 ounce letter domestically. The rates for postage increased as of January 2014.
Larger postcards, such as a 6 x 9 postcard, require a 47 cent stamp, but when you mail more than 5,000 postcards, the Standard Mail Presort rate is only 26 - 32 cents per postcard (exact rates depend on the addresses contained in the list) saving you 19 cents or more in postcard postage per piece!