Stupid HP-41 question

[Monte Dalrymple]

While attempting to convert (argh, now I remember why I tell everyone not to try to use the connectors that look like styrofoam in the middle) another of my machines to a CL last night, I happened to set it down next to another of my machines. Am I imagining things, or are the keys a dark grey rather than the black of all of my other machines? This one has a serial number starting with 2402S. My machines with serial numbers starting 2236S and 2427S (and others) have keys that are black (and had the "good" kind of connector.) Is there a correlation between the connector type and the key color? And why have I never noticed this before?