Does anyone know when the HGK DE 61 paint/livery changed to include the "EU arrow" with yellow stripe (as in soon-to-be-released ESU 31271)? Some photos show this was not the original livery.

When we visited Bacharach am Rhein in 2004, HGK was running class 66 frequently. But mostly south, mostly Rechtrheinstrecke, and mostly gray or black. We called them "Gray Ghosts" because they appeared/disappeared so quickly and silently.

As best I can determine, it appears that HGK DE 61 and 62 were delivered from GM-London, Ontario, Canada in Sept 1999 ORIGINALLY in red with the "EU arrow", with a white stripe along the bottom side of the cab instead of the current yellow, but with different numbers 9901 and 9902. These were the first class 66/GM model JT42CWRM locomotives outside Great Britain. They were leased to HGK by GM/Opel Leasing. They were purchased by HGK in June 2000 and were repainted with yellow stripe or new numbers either at that time or a few months earlier or later. DE 61 got the yellow stripe, DE 62 retained its white stripe as late as 6/4/2015.

works number 998101-1. 9902 DE 61
works number 998101-2. 9901 DE 62

There is a picture of 998101-2 at mainlinediesels.net dated 9/9/2000 showing the original livery but I have been unable to find a comparably early picture of 998101-1/9902/DE 61. The earliest photo I have found of that locomotive is dated 6/28/2002

You may be correct about the "Gray Ghosts" we saw at Bacharach in 2004 although I remember them as dark rather than the light gray Crossrail seems to use today. In any event we saw at least two red/EU arrows, some dark gray, and at least one black (MRCE/Mitsui Rail Capital Europe?). And after 2000 HGK purchased more GM class 66s some of which had gray or black livery.