In the Preferences window (Windows > Settings/Preferences > Preferences), Display section, ensure that Render swatches (startup) is enabled.
If the pause materials and textures swatch generation button is set to , toggle the button to to enable swatch rendering.
Increase the maximum resolution setting for swatches. In the Preferences window, Display section, select a higher resolution from the Max res. for swatches drop-down list.
You can also render an individual swatch by right-clicking the swatch and selecting Refresh Swatch from the marking menu.
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