private void addLocalVariablesHighlight(String text, int cursorTextOffset,
			VTMarkupItem localVariableMarkupItem, ArrayList<Highlight> highlightList) {

		if (localVariableMarkupItem != null) {
			int startIndex = 0;
			int endIndex = text.length() - 1;
			if (endIndex >= 0) {
				Color highlightColor =
					getMarkupBackgroundColor(cursorTextOffset, localVariableMarkupItem, startIndex,
						endIndex);
				Highlight highlight = new Highlight(startIndex, endIndex, highlightColor);
				highlightList.add(highlight);
			}
		}
	}
Creates a darker shade of the color passed-in, based on the given amount.

algorithm: 1) grab individual rgb elements
           2) multiply each by a factor.
           
           ie: int newRed = (int)(oldRed * 0.85);

@param color the color to shade
@param amount number between 0..1 (the smaller the number, the darker the shade)
@return the new color
Ghidra/Features/VersionTracking/src/main/java/ghidra/feature/vt/gui/duallisting/VTDualListingHighlightProvider.java