In Notes Standard Client, the background color for selected docs of Mail DB is fixed and can't be changed.
(The color of Notes 9/10 is navy blue and the color of Notes 11 is light blue )
Some users would like to change the color (e.g. Green) and others would like to display them same as Basic Client(the background color is transparent and the frame color is black)
Request the new setting in "Preference" - "Fonts, Colors and Themes" to change the background color (and frame color if possible) in Notes Standard.