{lusting: sofas with contrasting details}

I am a lover of piping on a sofa. The way that it outlines and emphasizes the shape of the piece is amazing. Currently I am swooning over those sofas with the contrasting square details on the backs ... no idea what to call them so here are a few examples:

source unknown

Style at Home

Style at Home

Style at Home

Any one know what these lovely square details are called or the source of these sofas? I know that the sofa in the last image is a William Birch piece, but I have no idea about the others and can't seem to find much info in my searching! Either way they are all lovely, I'd place a sofa like this on my dream home list for sure :)