How to prevent filter from decoding HTML

I’m busy writing a small filter plugin which should provide the WP tagline / blogdescription with some extra surrounding HTML.
So
‘Just another WordPress website’
could be changed to e.g.
<span style=”color:red;”>Just another WordPress website</span>

It works, however the problem is that the HTML is encoded to entities, whereas I need it ‘raw’ in order for the browser to executed the HTML.

This is what I have:

add_filter( 'option_blogdescription', 'add_html_blog_description' );

function add_html_blog_description( $option_value ) {
    $option_value = '<span style="color:red;font-size: 45px;">'. $option_value . '</span>';
    return $option_value;
}