For some reason, the 2.8 version of this isn't giving me the option of choosing yes or no for patterns. Other than that it seems to work fine.
Screen shot of the filter window...and yes, I have made the filter window longer to see if the tick box was over to the left, but it is not.

The color layer is automatically added with the chosen pattern. You can just make either invisible.

Preview windows in a SCM filter are not possible at this time. The plug-in would have to be either re written in Python or C. Python still couldn't show a preview but could run the filter in demo mode to show the results as you fiddled with the settings on the dialog. Not sure someone will want to re write it in Python though. You could ask.

But how do I get just the bright color with no pattern??? Somewhere back in this thread I thought I saw where there was a tick box for pattern or no pattern

Nope it wasn't added with an TRUE / FALSE argument option. I have fiddled with the code and now the results look like this. I also have the layers pattern-fill and the white layer invisible upon the scripts completion.

No more shadow which i thought took away from the results. It just seemed to take away from the sharpness of the results imo. I usually will tweak certain filters to my own liking. I encourage folks to learn and do the same.