There is no way to give it directly I think. You can do something with following python code:

import datetime
current_date = datetime.datetime.now().date()
new_date = current_date + datetime.timedelta(days=7)

Using that you can do it in 2 ways I think:

1. One is by overriding the fields_view_get(), which is triggered automatically on opening any views. You can refer "account_invoice.py", to understand that function and using the python code you can alter the tree view based on condition.

2. Second one to keep a boolean compute field and in the function you can check if date is greater than current date + 7. If yes, you can set it true. Call that field in tree view (hidden). For eg:

in your .py file:

import datetime
import dateutil.parser
from openerp import models, fields, api
class sale_order(models.Model):
    _inherit = 'sale.order'
    
    check_date = fields.Boolean(compute='_check_the_date')
    
    @api.depends('date_order')
    def _check_the_date(self):
        cur_date = datetime.datetime.now().date()
        new_date = cur_date + datetime.timedelta(days=7)
        for rec in self:
            order_date = dateutil.parser.parse(rec.date_order).date()
            if order_date > new_date:
                rec.check_date = True

in your xml file:

<record id="view_order_tree_inherited" model="ir.ui.view">
            <field name="name">sale.order.tree.inherited</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_tree"/>
            <field name="arch" type="xml">
            	<tree position="attributes">
            		<attribute name="colors">green:check_date==True;grey:state=='cancel';blue:state in ('waiting_date','manual');red:state in ('invoice_except','shipping_except')</attribute>
            	</tree>
                <field name="state" position="after">
                	<field name="check_date" invisible="1"/>
                </field>
            </field>
        </record>

Hope this helps!