Have you tried making the environmental light brighter? A white object in a dark room would always look gray.
"At night all cats are gray" as we say in Germany...
If you don't work with bloom, try to switch the appearance type to "Generic" and change the color for "Emission" to light grey. Change "IOR" to 3 and decrease the values for "Roughness" to about 2. This works fine for me.
Greetings from Hamburg,