Painted on Borders usually fail....sometimes badly...to effectively frame a screen. One issue being the ability to get a precise edging between the different painted surfaces. The other being that even with multiple coats of a Black paint, when the paint is applied to a flat surface, the reuslting degree of sheening allows any over spill of the image to be too easily seen when the projected content is of any brightness.
I've found that using thin MDF "primed Baseboard" Trim (3/8" - 7/16" x 3.25") keeps the "stand-off' from the wall from being too great (3/4" thick Trim is way overkill) yet the slight rise at the screen's actual "viewable" perimeter edge does allow a degree of "upward image crawl" at the vertical edge that can accommodate slight amounts of over spill coming from excessive zoom sizing, slight miscues in formatting, and key stoning irregularities that cannot be corrected.
The Disney Color "Mouse Ears" is about as good a non-reflective Black as can be found, yet it will reflect directed light. If you save a bundle by painting the wall, it would seem prudent to go the extra mile with the Trim, get the MDf, and some very affordable Triple Plush Black Velvet....,http://www.syfabrics.com/View.aspx/P...Velvet/681/264
.....and wrap & staple it onto the Trim.
You could Miter or Butt the trim at the corners. (...if you "Butt" you should trim off the baseboard's "curve"...) Hanging such trim onto the drywall is as simple as driving some 2' bright Finish nails through it into a few of the available studs, and the rest simply through into the Drywall. Set those nail heads with a nail Set/Punch to a point below the surface of the velvet.http://www.avsforum.com/avs-vb/showt...218&highlight=
Nothing else remotely affordable exists that can equal the light absorptive qualities of the proper type of Black Velvet, and look (...and feel...) so good doing it. Only the Self Adhesive Telescope Flocking material called "ProtoStar' equals/excels over Triple Plush Black Velvet,http://www.fpi-protostar.com/flock.htm
...but at $75.00 per each 30" x 200" Roll, it comes in at over $50.00 more expensive that velvet....$35.00 more if one factors in the cost of the MDF Trim @ $0.60 lf
Your trim is your finishing touch. Don't scrimp on it lest your DIY project wind up looking....well, too "DIY" .