Two ways to set Page Grid Settings.
Active Graph/Layout, Format: Page Grid Settings/Grid Settings
Graph/Layout page level mini toolbar: Show Grid: Page Grid Settings/Grid Settings
Set the offset and horizontal/vertical spacing of grids in cm or inch.
System variables to set grid colors:
@gc=color(255,128, 128, 1) //set layer grid color in Graph window
@gcp=color(255,128, 128, 1) //set page grid color in Graph window
@gcl=color(255,128, 128, 1) //set grid color in Layout window
Note: the 4th argument in color() function must be 1 to set these system variable with RGB colors.