The notebook colors are a sidetrack from the real issue which is that the color values returned from class {EV_STOCK_COLORS} are inconsistent across platforms. With GTK if I set my button background using {EV_STOCK_COLORS}.color_dialog it gives me what I want. I can check that this is not just a coincidence by changing the dialog color in the desktop preferences.

The problem with Windows is that most Win 7 themes (with the exception of Classic), tabs and tab containers do not correspond to the dialog color. (Some how it is propagating even though I did't call propagate_background_color) I don't know where else Windows 7 applies this notebook tab color. If it does appear elsewhere perhaps it can be considered as the default background color in which case {EV_STOCK_COLORS}.default_background_color should be amended. If not I would suggest introducing a new stock color: {EV_STOCK_COLORS}.color_tab_background.

It is only because the stock colors are inconsistent that I was looking for workarounds by querying instances of EV_NOTEBOOK or EV_BOX.

In the short term I might use {EV_STOCK_COLORS}.color_read_write as a workaround. It seems to match the tab color on most themes. I have a way of detecting the Classic theme and putting conditional code.