如何选择颜色并在Laravel上保存为RGB？

I am trying to store RGB value in the database (like "255,255,255" for my laravel project. So that I can use it on a custom style of a div. So far I only found this code to select color in form. (which stores as hex)

{{ Form::input('color', 'color', null, array('class' => 'input-big')) }}

Problem for me is that I want to use the color as RGB so that I can use it with different opacity levels:

background: linear-gradient(rgba( {{ $post->category->color . ",0.5" }} ) 0%, rgba( {{ $post->category->color . ",0.25" }} ) 100%);