Custom color ramp from text file in QGIS 3.26

Question

I want to write a text/xml file that will serve in QGIS 3.26 as a discrete colormap of a vector layer by one of its fields (using Symbiology->Categorized):

The field mentioned has 100 values but I want to specifically assign unique colors only to 3 values ,the other 97 values should be mapped to a single color as follows:

1. 'Spain' should be mapped to RGB value (120,34,25)
2. 'Italy' should be mapped to RGB value (12,238,45)
3. 'Romania' should be mapped to RGB value (127,100,200)
4. All other values should be mapped to RGB value (0,0,0)

How do I achieve this?

Answer 1

In the layer styling panel, for Fill color, use data driven override > Edit and insert this expression (see below for color values from a separate table):

case 
when NAME = 'Spain' then '120,34,25'
when NAME = 'Italy' then '12,238,45'
when NAME = 'Romania' then '127,100,200'
else '0,0,0'
end

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If you already have a separate table with the color values, make a table join to add the color information attribute field to your vector layer. Then simply use the name of the joined field as the expression and set fill color (for all other countries) to black.

Table join

Setting the attribute fieldname in data driven override for Fill color: