[SOLVED] Transparent background - not completely transparent

I've implemented sIFR 3 on my site but I'm having a strange issue.

The header is overlaid on a background image which is a gradient. This image is defined in the CSS. As you can see in the image below, the area covered by the sIFR is a slightly different colour.

~~Header image~~ (Dead Link)

The code for the replacement is as follows:

sIFR.replace(Amasis_MT_font, {
    selector: 'h1.flashHeader',
    css: [
    '.sIFR-root { font-weight:normal; color:#507A9A; leading:-10; width:500px }',
    'a { text-decoration: none }',
    'a:link { color: #507A9A }',
    'a:hover { color: #003366 }'
    ],
    wmode: 'transparent'
});