I'm getting this variance with color and light/contrast level in the diffuse in UE4 with the default scene and having turned off most or all of the post processing stuff in the viewer already. Turning off the spherical reflection thing helps but only pushes it about 10% to 20% of the way. Disabling all the lighting doesn't…
You can see that the "hue change" is coming from the diffuse lighting. The one in the viewport is more blue-ish, most likely because of a skylight and a skysphere setup. The material editor has a certain cubemap and lighting to it, and I'd assume he doesn't have the same lighting in the level. Also make sure that you have…