color mix in a html table

Use CSS to style your table.
Use "background-color" property and assign different colors to different rows.
So something like:
<table>
<tr>
<td class="tdRed">&nbsp;&nbsp;&nbsp;&nbsp;</td>
</tr>
<tr>
<td class="tdYellow">&nbsp;&nbsp;&nbsp;&nbsp;</td>
</tr>
</table>

The CSS will be:
.tdRed
{
background-color:Red;
}

.tdYellow
{
background-color:Yellow;
}

PS: I have intentionally checked 'Ignore HTML n text' so that you can see the 'nbsp' thing.

Another option is to create a colour gradient and use it as an image.

This[^] is an option.

I think you looking for gradient check the below link will help you solve issue.
CSS Gradient background with out image in table[^]