As far as I know, there is no way to do that. I'm not sure if this option is available on the 8330, or on your os but on my 8900 (OS 4.6) under options - advanced options - accessibility, there is an option to reverse the contrast of the colours that helps pplk with vision problems. I'm not too sure how this might apply in your situation, but you can give it a try.
Posted from my CrackBerry at wapforums.crackberry.com