Here's a picture of Willie looking a bit clapped out and possibly rusty, showing that such a paint-job on a model isn't actually wrong (can't see the rust levels on the turret hole cover, unfortunately, Carlos). I am convinced the date on that caption is wrong, though.

Here he is earlier, looking a bit more pristine, and still sporting the natty rear wheels...

As I said, I don't think that date can be right on the first photo. Number One Lincoln Machine (the turreted version with different tracks that later became Willie) only
started its trials in September 1915.
Couldn't have gone from this...

...to that first picture in a matter of days.