Yes, you need to do it within SkinStudio. You should be able to download SkinStudio from your Stardock account if you haven't yet.
Apply the skin that you are wanting to edit. Open SkinStudio and from the menu line click File/Open current WindowBlinds skin. Then select the substyle you're wanting to change if applicable.
Click on Edit Startmenu and Taskbar, then click on Edit Horizontal Taskbars.
Click on Background. Then click on the Extra settings tab at the bottom. Then click on Background effect. "Blur" will be selected, select Semi transparency instead. Then click on "Apply skin" towards the upper right, then "yes" on the "Save changes?" prompt that appears. The blur should be gone from the taskbar.
You will probably also want to remove the blur from the Window frames. Similar process, different section:
You will probably also want to remove the blur from the Start menu. Similar process, different section. For the Start menu though you want to remove it from 5 different subsections - Start Menu/Top part, Left hand side/Programs list, Left hand side/Bottom bar, Right hand side/Places list, All programs/Background:
(Love the new image uploading)