There is no ARIA folder here: ../extjs-6.5.3/build/packages/ux/classic/
so to be able to use Ext.ux.colorpick.Field it requires to apply at least classic styles:
Code:
<link href="../../../extjs-6.5.3/build/packages/ux/classic/classic/resources/ux-all.css" rel="stylesheet" type="text/css"/>