For me, Dark-backed should be much darker above, with a different head pattern (darker crown uniform with cheeks). Also the wing pattern (pale fringes to primaries) and tail pattern look wrong for Dark-backed.
Most aspects of this bird look closest to Beautiful for me. The only real problem I think is the apparent paleness of the underparts. As Matthew suggests, that may be related to the lighting on the photo. A few online photos show Beautiful also appearing to have pale underparts, e.g.:
http://orientalbirdimages.org/se ... y_ID=&Location=
http://orientalbirdimages.org/se ... y_ID=&Location=
