One way is to back out in the CSS inspector tool and find what other classes or tags apply to the current situation, and create styles based on that. For instance, for the search box, it appears that :
div.tc-sidebar-lists .tc-search-results a.tc-tiddlylink {
color: blue; }
will make search results blue.
But if you want to make a lot changes, and and want things to work together, it might be better to make your own colour palette. Under the tools tab on the right hand side you can find a button for colour palettes. Experiment to find which one is closest to what you want. The palette you last selected can be found inside
$:/palette. Open the one you like as a tiddler, clone it, and change the name and description fields at the bottom. Then see how things work by changing colors of various attributes.
For instance, you can change the color of the sidebar, both for search and for menu linking in the sidebar by changing this attribute:
sidebar-tiddler-link-foreground: red
Using the colour palette button from the tools tab again, you can make your palette the one currently in use.
In this way you can customize your TW and quickly apply it to other TW5 files that you make.
Good luck,
Mark