Formatting Hyperlinks

Me again! You folks have been so awesomely helpful!! 

And so I have another question. I would like to change the color of the text that shows a hyperlink has been clicked on already...it has defaulted to aqua and I would like to change it to something that will contrast more with the background. I know this is probably very simple to do but I have spent a lot of time looking already, so I thought I'd check with the experts.

Thanks!

Shari  :-)