To change the icon color to yellow when available quantity less then five you need to replace div named "sale_stock,qtyAtDate" defined in sale_stock.xml file of sale_stock module which you can find in odoo addons.

<div t-name="sale_stock.qtyAtDate">
<div t-att-class="!widget.data.display_qty_widget ? 'invisible' : ''">
<a tabindex="0" t-attf-class="fa fa-area-chart {{ widget.data.forecasted_issue ? 'text-danger' :
widget.data.qty_available_today > 5 ? 'text-primary' : 'text-warning' }}"/>
</div>
</div>

Jainesh, thank you for your help - this works.

I actually knew that location of this line is in sale_stock.xml but I tried to change it via my module that would replace this div.

In my module I created xml file with this code:
https://ibb.co/gvms55p

Unfortunately it didn't change it - I must be doing something wrong here with inheritance :/
Do you know how to make this work in my module? Thanks.