Obtaining a list of unique values

Given an XML file that contains a list of Items each having an attribute
Colour with its value,
is it possible to obtain a list of all unique colours of Items.

For example if XML looks something like this:

<Item name="item1">
    <Field name="Colour">
        <Value>Red</Value>
    </Field>
</Item>
<Item name="item2">
    <Field name="Colour">
        <Value>Blue</Value>
    </Field>
</Item>
<Item name="item3">
    <Field name="Colour">
        <Value>Red</Value>
    </Field>
</Item>

Then I would like to obtain a list containg exactly two entries:  Red, Blue

Thanks!
Sasa C.


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