Hi,

You can try the following steps for getting color to one2many field

Include your one2many field inside a div like below

<div class="background_black">
    <field name="order_lines" attrs="{'readonly': [('state','!=','draft')]}"
           style="background-color: #404040 !important;">
        <tree string="Laundry Order Lines" editable="bottom"
              decoration-info="state == 'draft'"
              colors="grey:state == 'done';black:state == 'extra_work';green:state == 'wash';">
            <field name="product_id"/>
            <field name="description"/>
            <field name="qty"/>
            <field name="washing_type"/>
            <field name="extra_work" widget="many2many_tags"/>
            <field name="state"/>
            <field name="amount"/>
        </tree>
    </field>
</div>

Here one2many field name is order_lines and assign a class to div, in the above case it is background_black.

Now we have to define style for this div class in a css file.Define template for including the style file

<template id="assets_backend_tablet" name="Field Background" inherit_id="web.assets_backend">
    <xpath expr="." position="inside">
        <link rel="stylesheet" href="laundry_management/static/src/css/background.css"/>
    </xpath>
</template>

laundry_management is the module name, you can use your module name.And define style like below

.background_black .o_list_view{
        background-color: #404040 !important;
}

And we can get the one2many field like below

Hope it helps