Stuck with select distinct

Hi All

I'm trying to get a list of distinct items from an XML. I've done this many
times using a predicate containing a preceding axis, but this one has got me
stumped:

<page>
        <front_back>F</front_back>
        <page_no>1</page_no>
        <colours>
                <colour>Red</colour>
                <rgb>00FFFF</rgb>
                <colour>Green</colour>
                <rgb>00FF00</rgb>
                <colour>Blue</colour>
                <rgb>FFFF00</rgb>
        </colours>
</page>
<page>
        <front_back>F</front_back>
        <page_no>2</page_no>
        <colours>
                <colour>Green</colour>
                <rgb>FFFFFF</rgb>
        </colours>
</page>
<page>
        <front_back>F</front_back>
        <page_no>3</page_no>
        <colours>
                <colour>Green</colour>
                <rgb>00FF00</rgb>
        </colours>
</page>

I need to return a nodeset with a list of DISTINCT colour nodes, that I can
then process in a for-each element.

The other conditions for selection are:

    colour is not Red or Blue
    rgb value is not FFFFFF


I somehow need to combine the following predicates (I think)

    colours/colour[. != 'Red' and . != 'Blue']
    colours/rgb[. != 'FFFFFF']
    colours/colour[not(. = preceding-sibling::colour)]

I'm stuck with XSL 1.0 and would like to avoid using keys if possible

Any suggestions greatly appreciated

Regards

Mark