How can I display multi list from dynamic drop down list

Hello,

I have a product page and would like to add a number of drop down forms to sort and display only the ones selected.

I have a form like this which does only show the items:

<form action="/product-page.php"><select name="colour" onchange="this.form.submit();">
<option value="*" selected="selected">Select Colour</option>
<option value="Yellow">Yellow</option>
<option value="Red">Red</option>
<option value="Green">Green</option></select></form>
<form action="/tigi-bedhead.php"><select name="colour" onchange="this.form.submit();">
<option value="*" selected="selected">Select Colour</option>
<option value="Yellow">Yellow</option>
<option value="Red">Red</option>
<option value="Green">Green</option></select></form>

This changes the url to something like: /product-page.php?colour=Red
and does actually only show the red items in the multi-list.

However I would like to do two things.
1. When you say select Yellow and it shows Yellow products, it also keeps Yellow in view on the drop down.
2. Can the items be dynamically added from products with the colour selected? Say if I have 10 items that are blue and 2 red items the drop down list knows there is a least 1 available to show and adds it to the dropdown list - if there are 0 brown items for example, the list doesn't include brown as an option?

Is it also possible to add further drop down lists for the visitor to select things like conditioner, shampoo etc. and brand - what I mean here is, can I add as many drop down list as needed?

Thanks Jono