One of the things that can be hard to read in Vista is the labels under the icons you have on your desktop (if you have icons on your desktop).  By default, they will have a shadow to try making them stand out from the background.  With some backgrounds this can make them hard to read.

To enable or disable this feature, you would go to the "Performance Inforamtion and Tools" option in the Start - > Control panel.  Then click on the "Adjust Visual Effects option on the left side.

You will find the shadow option around the bottom of the list.

While you are there, you might find other options you may not want enabled.

Another area of interest is changing the color of the text label under icons on the desktop along with other colors.  Windows does not provide a method to actually change the color of the text.  It is either black or white depending on the color of your background, if it is a dark background it will be white, if it is a light background it will be black.  

You can change your background color by going to Start - > Control Panel and clicking on Personalization.  The first option "Window color and appearance" and then select "Open clasic appearance properties for more color options", and click "Advanced".  Then select Desktop (should be defaulted there when you open the window).  You can change the desktop color there.

There are some third party applications that allow you to change the color directly.