When generating responsive images, the media library will generate a tiny version of your image which will be used for progressive image loading. By default this tiny version will be blurred version of the original.
You can customize how the tiny version of the image should be generated. Maybe you want a to just use the dominant color instead of blur. In the responsive_images.tiny_placeholder_generator of the media-library config file you can specify a class that implements Spatie\MediaLibrary\ResponsiveImages\TinyPlaceholderGenerator. This interface only requires you to implement one function:
$sourceImagePath contains the path of the image where you should generate a tiny representation for. The generated tiny image should be saved at $tinyImageDestinationPath. This tiny image should be a jpg.
Here's a an example implementation that generates a blurred version.