I'd go with your dad's notes. The only color photo of the Jacks Cabin tank I've found is one with the tank at a distance, with the scrap train picking up the rails. It's on page 141 of the 1989 issue of _Trails Among the Columbine_. Photo credited to Robert A. LeMassena, and yes, the oft repeated myth about the tank being moved is included in the caption. The image is not a photo print, and the color of the tank body appears to be mostly weathered wood, not D&RGW "Jersey Cream" (buff), but perhaps the paint didn't adhere well. The shingles appear to be an almost pinkish color - but IIRC, red composition roofing was popular at that time. As I say, it's really not easy to say from the photo, so I would take the notes of Cliff Grandt taken at the time as the best indicator of the correct color for this tank.
The latest Iron Horse News reports the Colorado RR Museum has a near replica now replacing the old No Agua tank. The image in the IHN seems too yellow to be a completely accurate color, but perhaps this is the printing process, or maybe just the luck of the available paint. I think the Behr brand paint I used on my garage is much closer to the D&RGW Jersey Cream building color than the yellow on the new CRRM water tank.
Charlie Mutschler
-30-