1. For each option, how do you know what the color should be?
2. How do you want to color it? Background of the table cell? Of the label?
3. Are some of the colors dark? How will you deal with black text on a dark background? As an alternative to a background color, how about a small square somewhere close that uses a color? That way it will not conflict with the text.
Before you can use Javascript to change the color, you need to decide what the coloring will look like using HTML and/or CSS. Then you can write Javascript to create the same effect dynamically.
Add the following row to the table:
<tr>
<td>Demonstration</td>
<td><label>
<select class="textfields">
<option id="0">Select One</option>
<option id="1" selected>A</option>
<option id="2">B</option>
</select>
</label>
</td>
</tr>
Now modify that so that it has the right color (background color, square, whatever) when the page loads. What is the new markup that shows the coloring?