The black does have a purpleish tinge on my panels, but the other colours don't. Overall it's pretty low contrast and saturation, and unable to reproduce cyan or fuchsia even with blending through any kind of blending, which makes certain things like sky and water come through poorly.
The similar project I'm working on is looking like it'll get about a year of battery life with a typical 18650, the 5.65" version of the display and run off an ESP (refreshed once a day).
I made a palette for colour space conversions for reference: https://imgur.com/a/2vgFsT4