I understand going into Layout > Page Background > Solid Fill, however this only changes it for the current document. I considered setting an action to change it for every document - but this is sill cumbersome and doesn't always work well.
Under customization
This only changes the area around the artboard.. Looking to find an application wide change to be able to have the default white space of an artboard to be slightly grey instead.. This doesn't achieve my goal, but thanks for the tip.