Dropdown Menu Widget version 1.9 is released today. With version 1.9, I added the ability to change arrow colors now. You can change your parent item arrow colors in the options panel.
I also added 2 new themes to the plugin: Pills and Rounded corners. I’m sure their colors won’t fit for most sites out there, but you can customize those stylesheets and save them to your theme folder named
dropdown.css This way you will have a custom dropdown theme, which you can then select from the options page. It will be added to the drop-down menu theme select box.