Covered Hopper

The New Haven Railroad had AC-2 Covered Hoppers but, didn't have PS-2 Covered Hoppers.
What difference is there between the AC-2 and the PS-2 Covered Hoppers ?

AC-2 I think was an unofficial designation given to AC&F's 1958 cu ft covered hopper. Similarly D&H termed their Greenville built 2003 cu ft cars GV-2s.

NH had both AC-2 and Pullman-Standard PS2 cars. Some of the AC-2s were assigned to sand service out of Tremont, MA while the rest were in cement service out of the Lehigh Valley (L&NE).

was that the difference in the paint schemes? i assume the brown ones were for sand and the grey for cement

I posed that question myself a while back on this forum. I assume yes, I have a some waybills that show many sand hoppers from Tremont billed to Hopedale, MA. The numbers correspond to the numbers on the brown cars as decorated by Bowser. On the flip side, I've never seen one of these numbers on a photo of a gray car. Assuming Bowser got the numbers correct, I'd say the color was used to help differentiate the two groups of cars (Brown = sand; Gray = cement).