Hi Troy,
It seems that there are two highlights on the example image.
There's the syntax highlighter, which you should be able to switch off by turning the syntax highlighter to "None".
You can do that from the menu, go to "Tools" -> "Highlighting" and select "None".
Second highlighed text is a selected text, where matching text is highlighted in yellow. This is not optional, I think, but you can change colour to something less bright. Go to "Settings" -> "Configure Kate", then to "Fonts & Colours", and your offender is "Search Highlight". Change to your liking, or match with "Text Area" colour to remove it.
Hope this helps.
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Piotr Gbyliczek
Solutions Engineer (LPIC 3, Novell CLA, RHCE, Azure, AWS certified)
Node4 LTD