Penny Red stamp was issued in 1841 to replace Penny Black stamps. Mainly because red seal in black stamp was not visible enough. Black seal on Red stamp worked great so it was in use in Great Britain and Ireland until 1879. As to records more than 21 billion Penny Red stamps were printed.
Value of these stamps are varies. The plate 77 Penny Red stamps are probably the most valuable since only 9 stamps are known to exist. Recently one stamp was auctioned for more than half million pounds (over one million USD).