<tree colors="red:notes!=False'">

Take a look at an existing XML definition of a treeview that uses colors for more help.

Hi, try this example...

In py file

'status' : fields.selection([('single','Single'),('married','Married')],'Status?'),

In xml file

<tree string="Status" colors="red:shop=='single';green:shop=='married' "> <field name="name"></field> <field name="status"></field> </tree>

For Odoo 11 in original view:

<tree decoration-success="state=='done'" decoration-success="state=='undone'">

...

</tree>

on inherited view:

<xpath expr="//tree" position="attributes">

    <attribute name="decoration-danger">approved == False</attribute>

    <attribute name="decoration-bf">approved == True</attribute>

   <attribute name="decoration-success">approved == True</attribute>

</xpath>

If you want to compare several values or make operations you can also do something like:

<tree colors="blue:state == 'draft';black:state in ('proforma','proforma2','open');gray:state == 'cancel';orange:date_due &lt; current_date;" string="Invoice" default_order="date_invoice">

take note that in xml you can not use <, >, >=,<= because that simbols are part of the structure, so instead use &lt;, &gt;, &lt;= and &gt;=

Using a decoration tag is a better idea!
There are many defined colors for decoration and we can apply them based on conditions in  tree as well as in fields

I would make it with custom web module.

JS: RPC call with list of ID's from each row from listview

Python controller: response with list of ID's what have note field not empty.

JS: change color for this ID's

If you wanna combine two decorators, can use "or" and "and" operators in the decorator, for example:

decoration-success="state=='offer_received' or state=='offer_accepted'"

For Odoo13, Odoo14, Odoo15 

decoration-danger="color_definer=='0'"