According to this solution in this issue on github:

https://github.com/zenoamaro/react-quill/issues/188#issuecomment-294092442

i've successfully tried to change the bold button in the toolbar options doing this:

const icons = Quill.import('ui/icons');
icons['bold'] = <Bold/>;

<button className='ql-bold'>
        <Bold />
 </button>

But I want to change the color picker icon too, but instead of a button tag it is a select tag, and if I tried to do the same as the button code it won't work.