Wagtail/Django: How to pass a Page model object as a default value for a streamfield block?

Question

How can I pass the user selected value for background_color object that is in my PostPage Page class as the default value for another ColorField that's within my streamfield blocks?

class PostPage(Page):
    # The user selected value for background_color is the object that I'm trying to pass as a default for a streamfield block.
    background_color = ColorField(default="#000000")

    # streamfield in question
    blog_builder = StreamField(BlogFeatures(), blank=True)

    content_panels = Page.content_panels + [
        NativeColorPanel('background_color'),
        StreamFieldPanel("blog_builder"),
    ]
    edit_handler = TabbedInterface([
        ObjectList(content_panels, heading="Content"),
    ])

Here is my streamfield class that uses StreamBlock:

class BlogFeatures(StreamBlock):

    simple_list = SimpleList()  

I use a Structblock to help achieve my streamfield goals:

class SimpleList(StructBlock):
    ...
    # how can I set the default value of this background_color to match the user selected value from the Page Model called PostPage.
    background_color = NativeColorBlock(default="#ffffff")
    ...