when setting your xpages theme to oneuiv2.1_gen1 the background color is wrong...  It should be the blue background but it is an off white color.

 

this is the result of the <programdirectory>\xsp\nsf\themes\oneuiv2.1_gen1.theme setting the form styleclass to lotusForm  to fix the issue I commented out the following from the .theme file

    <control>
        <name>Form</name>
        <property>
            <name>styleClass</name>
            <value>lotusForm</value>
        </property>
    </control>

 

if you don't want to or can't edit the theme file you could always over ride the value in an application specific theme...