NWL : Here are the pictures of the 513 Observation and 515 Coach with the red roofs. You were correct there is "No Green" anywhere on the cars.
Here is the side view, other side is identical. I do have a second coach but it is the same as this one so I didn't include it.
I think these are about the least expensive passenger coaches Flyer made , my data (also from Greenberg) says manufacture between 1925 -1929
Here is the end view. The non-platform end of the Observation is exactly like that of the coach except it has 513 over the door. Both cars state..."Made in USA" in the lithography just under the number in the first portion of the yellow section. Another interesting feature is that cars are tab/slot (or more like tab / hoop) couplers but the tab coupler on the observation swivels as it is connected to the floor via a rivet. The couplers on the coaches are fixed although the hole for the rivet is present in the floor. I expect that the hoop provided sufficient side to side motion to allow the cars to go around a curve. I have seen these referred to as "Hummer" type cars although they were introduced somewhat later and are slightly longer. I have always assumed they were pulled with a Hummer type 3 mechanical loco.
Their method of manufacture is interesting to me as an engineer. The entire car except the floor , axles , and wheels is one piece of lithographed sheet metal. This one piece of sheet metal includes the observation platform on the observation car, it is not a separately added piece. Obviously lithographed flat then folded (like Origami) to make the car. Tabs are folded into slots in the floor to fasten the car to the floor. The journal boxes are part of the upper sheet and simply hold the axles via being positioned well in from the end of the axle.
Anyway there they are ... Red, Yellow, Black (no Green) enjoy!