Updated June 1st: First day postmarks:
Standard 4-bar FIRST DAY OF ISSUE
Digital Color Postmark:

from the Postal Bulletin May 27th:
On June 5, 2015, in McLean, VA, the U.S. Postal Service® will issue the Flannery O’Connor three ounce rate mail-use stamp (Non-denominated priced at 93 cents), in one design, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 118900).

The stamp will go on sale nationwide June 5, 2015.

The 30th stamp in the Literary Arts series honors Flannery O’Connor (1925–1964), who crafted unsettling and darkly comic stories and novels about the potential for enlightenment and grace in what seem like the worst possible moments. The color portrait on this stamp, a watercolor painting completed digitally, is based on a black-and-white photograph taken when O’Connor was a student at the Georgia State College for Women from 1942 to 1945. Surrounding O’Connor are peacock feathers, a symbol often associated with the author. The words “THREE OUNCE” on this stamp indicate its usage value. Like a Forever® stamp, this stamp will always be valid for the rate printed on it. The initial price and value for this stamp is 93 cents. Art director Phil Jordan designed the stamp with artwork by Sam Weber.

How to Order the First-Day-of-Issue Postmark:
Customers have 60 days to obtain the first-day-of-Issue Postmark: by mail. They may purchase new stamps at their local Post Office, at The Postal Store® website at http://www.usps.com/shop, or by calling 800-STAMP-24. They should affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

93¢ Flannery O’Connor Stamp
McLean Main Post Office
6841 Elm Street
McLean, VA 22101-9998

After applying the first-day-of-Issue Postmark:, the Postal Service will return the envelopes through the mail. There is no charge for the postmark up to a quantity of 50. For more than 50, customers have to pay five cents each. All orders must be postmarked by August 4, 2015.

There are seven philatelic products for the Flannery O’Connor stamp issue:

• 118906, Press Sheet with Die-cut, $111.60 (print quantity 250).
• 118908 Press Sheet without Die-cut, $111.60 (print quantity 500).
• 118910 Digital Color Postmark Keepsake, $20.95.
• 118916 First-Day Cover, $1.37.
• 118921 Digital Color Postmark, $2.08.
• 118931 Stamp Deck Card, $0.95.
• 118932 Stamp Deck Card with Digital Color Postmark, $2.43.

Technical Specifications:

Issue: Flannery O’Connor Stamp
Item Number: 118900
Denomination & Type of Issue: Three Ounce Rate Non-Denominated, Mail-Use
Format: Pane of 20 (1 design)
Series: Literary Arts
Issue Date & City: June 5, 2015, McLean, VA 22101
Designer: Phil Jordan, Falls Church, VA
Art Director: Phil Jordan, Falls Church, VA
Typographer: Phil Jordan, Falls Church, VA
Artist: Sam Weber, Brooklyn, NY
Modeler: Joseph Sheeran
Manufacturing Process: Offset, Microprint
Printer: Ashton Potter (USA) Ltd. (APU)
Printed at: Williamsville, NY
Press Type: Muller A76
Stamps per Pane: 20
Print Quantity: 20 Million stamps
Paper Type: Nonphosphored Type III, Block Tag
Adhesive Type: Pressure-sensitive
Processed at: Ashton Potter (USA) Ltd. (APU)
Colors: Black, Cyan, Magenta, Yellow, PMS 123C Yellow, PMS 696C Burgundy
Stamp Orientation: Horizontal
Image Area (w x h): 1.42 x 0.84 in./36.07 x 21.34 mm
Overall Size (w x h): 1.56 x 0.98 in./39.62 x 24.89 mm
Full Pane Size (w x h): 7.24 x 5.95 in./183.90 x 151.13 mm
Press Sheet Size (w x h): 21.72 x 11.90 in./551.69 x 302.26 mm
Plate Size: 240 stamps per revolution
Plate Numbers: “P” followed by six (6) single digits
Marginal Markings: Front: Plate numbers in four corners of pane 
• Header: Literary Arts 30th in a Series
Back: © 2015 USPS • USPS logo • Plate position diagram • Barcode (118900) in upper right and lower left corners of pane • Promotional text • Verso text

From the USPS May 26th:
The 30th stamp in the Literary Arts series honors Flannery O’Connor (1925–1964), who crafted unsettling and darkly comic stories and novels about the potential for enlightenment and grace in what seem like the worst possible moments. The color portrait on this stamp, a watercolor painting completed digitally, is based on a black-and-white photograph taken when O’Connor was a student at the Georgia State College for Women from 1942 to 1945. Surrounding O’Connor are peacock feathers, a symbol often associated with the author. The words “THREE OUNCE” on this stamp indicate its usage value. These Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use. The 93 cent Forever stamp will be issued June 5 in McLean, VA, at the NAPEX Stamp Show. Art director Phil Jordan of Falls Church, VA, designed the stamp with artwork by Sam Weber of Brooklyn, NY.

From the USPS May 18th:
The 30th stamp in the Literary Arts series honors Flannery O’Connor (1925–1964), who crafted unsettling and darkly comic stories and novels about the potential for enlightenment and grace in what seem like the worst possible moments. The color portrait on this stamp, a watercolor painting completed digitally, is based on a black-and-white photograph taken when O’Connor was a student at the Georgia State College for Women from 1942 to 1945. Surrounding O’Connor are peacock feathers, a symbol often associated with the author. The words “THREE OUNCE” on this stamp indicate its usage value. These Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use. The initial price and value for this stamp is 93 cents. Art director Phil Jordan designed the stamp with artwork by Sam Weber.

The first day of issue will be at the NAPEX stamp show in McLean, Virginia, on June 5th.

From Wikipedia:

Mary Flannery O’Connor (March 25, 1925 – August 3, 1964) was an American writer and essayist. An important voice in American literature, she wrote two novels and 32 short stories, as well as a number of reviews and commentaries. She was a Southern writer who often wrote in a Southern Gothic style and relied heavily on regional settings and grotesque characters. Her writing also reflected her own Roman Catholic faith, and frequently examined questions of morality and ethics.

O’Connor’s The Complete Stories won the 1972 U.S. National Book Award for Fiction and was named the “Best of the National Book Awards” by internet visitors in 2009.