An exhibit has one place the reader should look first. Deciding which place, then building the picture so the eye goes there without being told, is most of the difference between an exhibit that reads in four seconds and one that reads in twenty.
Attention is a ranking problem. With one accented element there's nothing to rank, and the eye goes straight there. With three, the reader has to compare three candidates against each other, which is three pairwise comparisons, and that happens before any thinking about the data. With five accents there are ten pairwise comparisons. By then the accents cancel each other out, and nothing on the chart stands out at all.
How do you create a focal point?
Five devices create a focal point, and they aren't equally strong. Position is the strongest and the cheapest. In a left-to-right layout the eye starts at the top left and works down and across, so whatever you put there gets read first, whether you meant it to or not. Contrast comes next: one saturated element against a field of grey. Then isolation, meaning white space around the element that nothing else gets. Then enclosure, a light box or band. Size comes last and is the least reliable, because on a chart the sizes usually encode the data, and changing them for emphasis breaks the encoding.
One exhibit's accent budget is one colour, one annotation and one direct label set. Here's how Turant's contribution-margin chart spends it. The line is a single mid-grey until the point it crosses zero, and from there it's in the accent colour. The annotation is one short phrase at the crossing saying when it happened. The label is the Q8 endpoint with its value. Nothing else on the chart is coloured, and the zero line is a thin rule with no highlight, because the colour change already carries the crossing.
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What goes wrong with too many focal points, and how to fix it
Now the failure, and it's worth counting. A first draft of the same chart carried six competing elements. Each of the eight quarters had a value label, the zero line was red, a shaded band ran across the negative region, and a second accent marked the Q5 point where variable cost rose. On top of those came a legend for a single series and a callout box holding the breakeven multiple. Six elements asking to be looked at first force fifteen pairwise comparisons before the reader does any thinking. And the one message, the crossing, is the only thing on the chart that isn't set apart from anything else.
Repair it by working backwards from the message. Name the message. Name the single element on the chart that carries it. Strip the accent from everything else, in this order: callout boxes, shaded regions, secondary point labels, the legend if there's one series, and colour on structural elements such as axes and zero lines. Then check that the eye goes to the surviving element. You do that by looking away, looking back, and noticing where you looked.
Is the title a second focal point?
There's a second focal point that's easy to forget. The title is on the slide too, and it competes. Put the title in the accent colour with a coloured element beneath it and the reader gets two things at the top of the page. What works is a title in the body text colour, with the accent saved for the exhibit. The reader reads the claim and then sees the evidence highlighted, in that order.