Check if field meets requirements before outputting CSS.

Based off the check_dependencies function, this disables a field from outputting in the 'head'.

Example:
A select with a list of stylesheets that when the user selects a value it hides all the color fields for certain styling. Once the fields are hidden they will continue to render their output into the <head> even though they do not meet their requirements and 'should' become in a disabled like state.