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.
I am shipping two postcards via first class mail in a regular letter size envelope. If I call it a package, postage would be $1.93 and it comes with a tracking number. If I mail it as a letter it only costs 49 cents but no tracking.