Setting colour for insensitive text

[tarnyko tarnyko net]

Hi folks, 

I have little problems setting colours for insensitive text in GTK entries. 
It used to work well with GTK+2, but with GTK+3 my choices seem to be 
ignored. 

Here is a Vala sample to demonstrate the problem :
http://www.tarnyko.net/repo/testgtk-insensitive_text.vala 

The important part is : 

Gdk.Color insensitive_color = Gdk.Color ();
Gdk.Color.parse ("red", out insensitive_color);
[...]
entry.set_sensitive (false);
entry.modify_text (StateType.INSENSITIVE, insensitive_color); 

I first instantiate a "Gdk.Color" object and parse the "red" colour in it.
Then I make my Entry insensitive, and associate insensitive text therein 
with my Color object. 

WORKS with GTK+2 :
valac --pkg gtk+-2.0 testgtk-insensitive_text.vala 

DOESN'T WORK with GTK+3 :
valac --pkg gtk+-3.0 testgtk-insensitive_text.vala 

Text is red in GTK+2, stays gray in GTK+3. 

Could someone give me a direction ? 

PS : I want to avoid using CSS if possible.