loading issue (colour)

Hi, I THINK this is a Hummingbird issue, but i'm not actually sure

I've been trying to improve the site load speed. When you load this site now, however, you can see that the menu bar loads in the wrong colour just for a second or two - perhaps due to the order in which things are now loading?

http://mksaccountancy.co.uk

Can't seem to resolve this and its an annoyance, would love a solution asap...

Thanks