[css-color-4][editorial] actually count correctly

Author: svgeesus

css-color-4/Overview.bs

@@ -3209,7 +3209,7 @@ Device-independent Colors: CIE Lab and LCH, OKLab and OKLCH</h2>
 		<img src="images/L-axis.svg" width=240 height=575>
 		<figcaption>
 			This figure shows the Lightness axis of the CIE Lab color space.
-			Twenty neutral swatches are shown (L=0%, L=5%, to L=100%).
+			Twenty-one neutral swatches are shown (L=0%, L=5%, to L=100%).
 			The steps are equally spaced, visually.
 		</figcaption>
 	</figure>