Sorry to say, but I think it's unlikely they're doing 64-level intensity grading. It appears they've reduced it from the DS2000/DS4000 series - perhaps to 32 levels maximum. I looked through the DS1000Z data sheet, and unlike the DS2000 datasheet which specifically mentions up to 256 levels of intensity in a couple of places, Rigol appears to have done something similar to GW-Instek (with the GDS-2000A datasheet) in that they don't mention ANYWHERE how many levels of grading the DS1000Z can do. Judging by your images, I can't say I'm much of a fan of what they've done with it.
Not a big fan of the changes to the screen design/colors either; I prefer the more subtle shading on the DS2000. I wonder if it's linked to the maximum amount of simultaneous colors they're using.
You should check how the intensity grading is functioning by sending the same AM signal into all 4 inputs simultaneously (or just using the 50Hz noise), making a screen capture, then counting colors in Photoshop (or similar) - as in the attached image.
Also, for the benefit of others, you might consider using a frequency counter on the Trigger Out and making a quick table of the waveform update rates (similar to the following from the DS2000):