Black vs White

Yes, it has an effect but probably negligible.

The newer dark colored RV's, likely have a much bigger impact.

APT wrote:
If your whole trailer where black, then maybe. But not the small surface area of the AC unit itself.

Does the additional heat around the unit itself impact the cooling efficiency?
In general my experience has been when it's really hot out a single 13.5 K BTU unit struggles to keep up, regardless of the color of the A/C shroud .

Can you temporarily cover the AC (leaving the vents open) with a white or reflective material to test your theory?

If your whole trailer where black, then maybe. But not the small surface area of the AC unit itself.

I'd assume a white cover would help but the majority of the work is the compressor and condenser removing the heat from the inside. I'd bet that the small differential in temperature of the AC parts underneath would not make that great a difference in the efficiency of the AC.

I have a Heartland and in temps above 90 degrees it struggles. It is 13.5 and think I should of upgraded to 15,000. Anything helps and white might help some.
I go to Riverside and it get hot as you know. Last year had same issues and if no shade is available would spray the unit down with water. It seemed to help somewhat, but going bigger and or second unit such as a portable unit may be an option.