Dave,

Having lived in New York State for many years, and having modeled the New York Central for a while, my recollection is that the NYC freight car color was toward the brown side of the spectrum.  I used the old Floquil "Boxcar Red" color on a brass caboose or two, and it looked pretty close to prototype.

I looked up the NYC Historical Society site, and there is a series of 4 articles on NYC cabooses here
https://nycshs.files.wordpress.com/2014/02/pages-from-1975q1.pdf . 
They also have links to various paint manufacturers' websites.  I looked at the pages for Model Master Acrylics (as an example), and checked out their brown tones.  It seems that the color would be closest to #4675 Rust (flat) or #4707 Earth Red FS30117 (flat), or a blend of the two.  You might look here: https://www.testors.com/product-catalog/testors-brands/model-master/acrylic-paint/bottles . 

Todd Sullivan