Following the diagonal (a translation operation) takes you to the real next unit cell - whereas the fake but convenient unit cell is a doubled centred one occupying a quarter of the swatch. The glide reflection lines are the green dashed ones here. When you follow one of those lines, you flip your elements over for every half cell of distance you cover - so it's a slide and flip operation for the glide reflection. Whereas a normal mirror reflection line (the solid blue ones here) flips things over in situ without a combined translation component.
I used part of the same combined colour scheme as the jazz one. Performing arts has been the appropriate big-tent grouping for a while but it's possible that the music subset may eventually have to branch out on its own (with collections being limited to 30).