[ubuntu] tweak a theme?

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http://ubuntuforums.org – I recently downloaded and installed GnomishDark theme and MyUnity, and when I go to google and type something in, it types in the colour white, so I cannot see it. also any search bar will be coloured in black instead of white. For instance, the search bar for ubuntu forums in the upper right hand corner is black and types in a darker black. Is there a way to modify this? (Hardware)