if you want total control over your CSS, you may want to go into the overall_header.tpl file and remove the entire <style> section. If you do that, all your styles will be determined byt the .CSS file (you'll have to uncomment the css file link in that same TPL file).
After that, I would check the source on that page you want to fix, find the input field where the text is too light, and see if it has a class on it. If it does, just change the color for that class in your CSS file. If it has no class, you will either have to change the text color for "input" (I think that tag is grouped with several others, near the top of the CSS file), OR.....
create a new class for that particular input field, and then open the .TPL file for that page and add your new class to the input field.
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