Icons for attributes

How to put icons for the "Filter by" for example, red (red square)?

Could you elaborate more on your question?
If what you want is to change the checkbox images in the Ajax Filters then you need to change the image checkbox.gif file.
http://themes.fashion.nop-templates.com/Plugins/SevenSpikes.Nop.AjaxFilters/Themes/Fashion/images/checkbox.gif

Hope this helps!

No
I think
http://themes.fashion.nop-templates.com/c/8/dresses
Atribbute by Color
that the text "red" replacing the red square (picture)

This is possible editing SpecificationFilter.cshtml and put in line 57

<li class="@specificationFilterItem.Name"> instead of <li>

Then, in css create a style with your color square and name it with the same name of your color attribute.

The css like this:

.White{
  background-repeat: no-repeat !important;
  background-position: left 3px !important;
        background-image: url(images/colors/white-square.jpg}

I make I have done so on this page:

http://seraphita.fontventa.com/c/4/novedades

I hope I've helped

Sorry for my english.

Great thanks!
It is not necessary to apologize. My English is also not good.
It is important that we understand each other.

I tried and I'm wrong somewhere.
I hope it is not rude. Can you send the parts of two files that you edit.

SevenSpikesNopUI.css

.product-page-size span
{
    float: left;
    margin: 0 8px 0 0;
}
.White
{
  background-repeat: no-repeat !important;
  background-position: left 3px !important;
        background-image: url(../images/whitesq.jpg)
}

SpecificationFilter.cshtml

                if (specificationFilterItem.FilterItemState == FilterItemState.Checked)
                {
                    filterItemCssClass = "filterItemSelected";
                }
                    
        <li>
             <li class="@specificationFilterItem.Name"> Cap color <li>
            <a class="@filterItemCssClass" data-option-id="@specificationFilterItem.Id">@specificationFilterItem.Name</a>
                </li>
            }
        </text>;
    
    <div class="block block-category-navigation">


If not, thanks anyway!