This code defines a new vtype for Extjs 3 for the definition of a color value type

ext3_color.js

Ext.apply(Ext.form.VTypes, {
  
  // Color vtype definition
  color:  function(v) {return /^#(?:[0-9a-f]{3}){1,2}$/i.test(v);},
  colorText: 'This field must be a valid hex web color.',
  colorMask: /[#0-9a-f]/i,
	
});

gistfile1.txt

...

new Ext.form.TextField({
  name: 'default_color',
  fieldLabel : 'Default color',
  xtype: 'textfield',
  vtype: 'color'
}),

...