ArtRage applies lighting to the layers, which can change the look between exports and imports.
There currently isn't a way to avoid this, but you can reduce the effect by ensuring paper has 0% roughness on all your layers.
And try to reduce the amount of swapping between applications if you can.
Super Secret bit... In the upcoming release of ArtRage there will be an 'undocumented feature'. Pressing <F5> will turn off all the lighting effects so you can work with just the pure colour in ArtRage.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"