My suspicion is that the greyish Brixtons you saw were actually completely new, maybe tried on in store, but not seriously worn. NatCXL will usually start off very pale, and then will patina "golden" with wear and care. CXL won't pick up rain spots either like cordo is prone to doing. Obviously you don't want the shoes soaked, but I wouldn't mind wearing mine outside when showers started. Brush them well, and hit them with some reno/meltonian/whatever, and you should be good to go. I think NatCXL is probably the easiest leather to patina in the quickest amount of time b/c of how little dye is used (if any).
And do post pics of the tassels!!