So I went to the curtain shop today. Tried different blackout fabric color variations of grey (tested with XGimi H1, which is a bit similar in brightness (slightly more) but I tested on normal, so not full capacity). Unfortunately there is no indication of the color code 
but I’ll post what I bought at the end:
The next was a slightly darker grey but the brightness was not good enough in a completely dark room (allowed me to test in the back ).
There is definitely a difference in the contrast compared to the white fabric or the white wall. The contrast was best on the darker grey, but the brightness was not, and although I could boost the brightness, I intend to use the projector outside, and would use the eco mode for the PPM cause otherwise on Presentation I might not have time for a full movie (if not with a power bank).
They’ll deliver it on Monday and I’ll get it sewed to prepare for the PPM . Will post images with the final product.