Why the Background is Beige?!

[StarUpJewelry]

Hi! Everyone
Why the Background is always Beige?! I use dome light with HDRI "Studio G". as well as for reflection and refraction I use Studio G
Material of background and plane white plastic, still the background is beige

[StarUpJewelry]

Something else the Ruby doesn't come out with its real red color, and I am using for that V-Ray materials