With your model, you pick KPIs from your measures (including ones in a measures table) and every name is checked before you copy the script.
A KPI needs a number, a meaning (is it good or bad?) and some context. A target or a comparison such as last year gives it meaning. The numbers are only for the previews; the DAX uses your measures.
Ways that fit what you want readers to get come first. Pick one to see how to build it.
Status colors are good, neutral and bad, the way Excel’s conditional formatting shows them. Card colors are everything else: background, text, lines and the accent. The previews above and the measures you build use them all. Change any color, or take them from your theme. An arrow always goes with a status color, so it never relies on color alone.
Ideas behind the options: KPIs and cards in Power BI by Data Goblins (number, meaning and context; SVG and core-visual KPI templates).