I notice that the backphone on the DEUS headphones is black, is it the same as the one on the XP WS1 wireless headphones, which is blue? Can I use the DEUS backphone with the WS1?

No the backphone on the DEUS headphones is not compatible with the clip systems on either the earlier or latest WS1 models.
On DEUS, the clip system for the earphone is different. It is very easy to unclip the earphone in order to replace just the backphone in case of wear. Remember that what we refer to as the backphone includes the flexible headband, the loudspeaker and the foam. It does not include the electronic unit which can be unclipped (the left earphone). See the photo of the backphone below.
The DEUS backphone is as flexible as the one on the latest blue WS1, and is black for purely aesthetic reasons!
On DEUS, the clip system for the earphone is different. It is very easy to unclip the earphone in order to replace just the backphone in case of wear. Remember that what we refer to as the backphone includes the flexible headband, the loudspeaker and the foam. It does not include the electronic unit which can be unclipped (the left earphone). See the photo of the backphone below.
The DEUS backphone is as flexible as the one on the latest blue WS1, and is black for purely aesthetic reasons!