I'm using IE8 on Win7 and none of your tags appear black on my PC. Perhaps you are referring to badges that you've earned? I've also checked my tags and likewise none of them are black.

If your tags are black, does this also occur with a different browser?

Honestly, I don't know. Are you looking at the badges? Those are another way of showing reputation, different to the points sytem. Badges reward specific desirable behaviours and come in Bronze, Silver and Gold reflecting how desirable the behaviour is and how difficult the badge is to obtain.

For example, you have earned the Enthusiast badge, a silver badge, which is awarded to someone who visits the site each day for 30 consecutive days. This badge rewards the bahaviour of visiting the site frequently.

I assume it's the badges you are referring to, because I'm not seeing an 'black' tags when I look at your user profile.

You can find a full list of the badges, how they are obtained, which of them you have been awarded and how many others have been awarded each badge by clicking on the Badges button at the top of the page.