There is a variable called colorButton_enableMore in the pzpega_ckeditor js file. 

Setting this variable to thru customer config like can show us the additional colors plugin as per CKEditor documentation.

I tried the below in userWorkForm HTML fragment, but didn't really help.

<script>       CKEDITOR.editorConfig = function( config ) {     // Define changes to default configuration here. For example:    config.colorButton_enableMore = true;         }; </script>

But I'm unsure where to set it in order to get it applied as I haven't seen platform allowing customization on CKEditor plugin to alter RTE behaviour.