html.fromhtml android color font from attribut

Question

I have an application with different themes accessible. The color of a part of the text may vary depending on the theme. But when I use a color attribute that varies according to the theme, the color is not correct: the text is written in black instead of the desired color.

the set color with "font color="#307CA4"" is ok but with font "color=?color_txt_red" not work. why?

Part of code used:

file string.xml :

<resources> 
    <string name="txt_show" formatted="false"><![CDATA[<font color="#307CA4" ><b>Liste des messages reçus : </b></font>Vous avez <font color=?color_txt_red>%d message </font>non lu]]></string>
</resources>

file color.xml :

<resources>
    <color name="red_1">#ff0000</color>
    <color name="red_2">#c3051f</color>
</resources>

file style.xml :

<attr name="color_txt_red" format="reference|color" />

<style name="theme_1" >
    <item name="color_txt_red">@color/red_1</item>
</style>

<style name="theme_2" >
    <item name="color_txt_red">@color/red_2</item>
</style>

part of file testMain.java:

int nbMessage = 0;
tv.setText(Html.fromHtml(getString(R.string.txt_show, nbMessage)));

image valid

image error

May anyone could help me, please? Thank you!