Not all colors can be changed in style.css

I have a question for the masters of all things WordPress.

Say I want to style my header’s search box colors… simple, just go into “design setup” or style.css and it’s easy to find an option to change the border & icon color… but, changing the color or font for the word “search” is nowhere to be found in style.css(or design setup).

furthermore, I’ve successfully found(and changed) almost all background or content area colors easily enough… but, there’s this one white background I couldn’t find to save my life… at least not in style.css.

What am I missing? Is there another file similar to style.css that contains the other color codes etc? Stuff that can’t be found in style.css but can still be edited to make minor changes like color?

I’ve gone through style.css a million times and changed every color listed. There are still areas of my site that haven’t been touched because their css doesn’t appear to be in the style.css file.

I’ve tried getting CSSUpdater, Dreamweaver, and Topstyle to work… but I can’t figure out how to keep the changes I’ve made in them. So, I’m stuck living with the unwanted colors, or figuring out how to FIND them in the editor so they can be altered.

PS – I’m actually using the responsive auction theme but it isn’t showing in the dropdown box below.