Use a case expression to style the color of an icon depending on a layer property?

Question

Using Openlayers 8.1.0, I've been trying to modify the color of an icon depending on a layer property but I can't get it to work.

Here is my layer constructor :

const marqueursTest = new ol.layer.Vector({
  name: 'marqueursTest',
  zIndex: 999,
  visible: true,
  source: sourceWFS,
  style: { 
          'icon-src': 'assets/cavage.png',
          'icon-color': [
            'case',
            ['==', ['get', 'roche'], 'calcaire'], [255,153,102],
            ['==', ['get', 'roche'], 'craie'], [255,230,72],
            ['==', ['get', 'roche'], 'gypse'], [153,255,102],
            ['==', ['get', 'roche'], 'autre'], [102,204,255],
            [226, 226, 0],
          ],        
  },
  opacity: 1    
});

The icon-src works but the icon color throws the following error :

Uncaught Error: Expected an array of numbers for icon-color

Am I misusing the expressions in this case or are they not supported for icon-color?

According to the doc, it should work but I may have made an error in the syntax since I'm not a professional developer.

Relevant doc and examples are below :

https://openlayers.org/en/v8.1.0/apidoc/module-ol_style_expressions.html

https://openlayers.org/en/v8.1.0/apidoc/module-ol_style_flat.html

https://openlayers.org/en/latest/examples/style-expressions.html