From what I understand, use the same colour as what you used for your ESB gauntlets. I'm using Humbrol 78 enamel through an airbrush to paint my JP. As for the yellow details, I think I might use Humbrol Insgnia Yellow 154, heavily weathered with some rust washes and pigments. I will also use PollyScale PRR Brunswick Green for the black detail stripes (like on the helmet). As for the red, I'm leaning towards a rusty red (likely a custom Tamiya Or Vallejo Model Color mix).
The white detail on the lower left side of the pack will probably be a custom decal I print on white decal paper.