[gtkada] Treeview: coloring the expander part of the expander column

[Juan L. Freniche]

Hello All,
Using modify_base (treeview, , state_normal, some_color), we are able to 
color the treeview background. Then, using for example
set_property (render, background_property, other_color) and pack_start 
(col, render, true), we are able to color the cells background.

However, the column containing the expander is colored in this way: the 
render part using "some_color" and the textual part using "other_color", 
i.e., using the color set by modify_base and not using the color set by 
set_property for the column.

The effect is not nice.

Is there any way to color the expander part of the expander column as it 
is made for other columns?