[IMP] theme_*: remove some snippets hard coded background color

This is the direct following of the PR [1].

Some themes "hard code" the background colors of some snippets, which
prevents the user to change it with a preset color without deleting the
current background first.

This commit does two things:
- remove the problematic hard coded background colors;
- replace the colors that are removed by some themes by the ones that
were set in [1] (for the searchbar and text highlight snippets).

[1]: https://github.com/odoo/odoo/pull/90749

task-2824393

closes odoo/design-themes#563

Related: odoo/odoo#90749
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

theme_cobalt/views/customizations.xml

@@ -159,7 +159,7 @@
 <!-- ==== Picture ===== -->
 <template id="s_picture" inherit_id="website.s_picture" name="Cobalt s_picture">
     <xpath expr="//section" position="attributes">
-        <attribute name="class" add="bg-o-color-3 pt72 overflow-hidden" remove="o_cc o_cc2 pt48" separator=" "/>
+        <attribute name="class" add="pt72 overflow-hidden" remove="o_cc o_cc2 pt48" separator=" "/>
         <attribute name="data-oe-shape-data">{"shape":"web_editor/Bold/01","flip":["y"]}</attribute>
     </xpath>
     <xpath expr="//section/div" position="before">