Open the form in the editor, select the area on your form and expand the brush category to the left. You should be able to set it however you want, less gray, get rid of the fill altogether, etc.

Unfortunately, in the classic forms editor there is no access to the object parameters therefore you cannot remove the fill.  However, you can delete the object with the shading.  Then select and copy the one around the Bill or Ship fields.  Then, right-click on the object and select "Sent to Back".  Finally, move and resize it accordingly.