If you are modeling in between 1930 and 1935, your car should probably be painted like this photo of #19 at Morrison (DPL 186750)
or this Circa 1933 CONOCO 8 on the C&S. (lad Arend Photo)
The cars seemed to use this paint scheme from about 1929 and 1935 when they were repainted Black. My opinion is that the under frames after the repainting was black. CONX 5 recieved a replacement underframe in the mid 1930's after a wreck destroyed the original frame. This is the frame modeled in the Classic Miniatures kit.
The Late John Maxwell was was asked about CONX Colors in 1975 here is his reply:
Since there was not many color photos taken in the early 1930's his comment that "you pays the money and you makes your choice" seems to still hold true. Green anybody?