Describe the bug
We can change the text & background colour for Paragraph Blocks within a cover Block, but we can't change the colours for a Heading block. This is inconsistent and makes no sense. If we can change the colour for one, then we should be able to change the colour for the other.

Depending on the overlay colour that's selected, you may render your Heading Block near invisible if you're unable to change both the background colour and text colour, like you can for the Paragraph Block

To reproduce
Steps to reproduce the behavior:

1. Add Cover Block
2. Insert Paragraph Block into Cover Block and change background/text colour
3. Insert Heading Block into Cover Block and try to change background/text colour

Expected behaviour
I expect to be able to change the background and text colour of a heading block, within a cover block, in the same way I can do that for a Paragraph Block

Screenshots
Paragraph Block within a Cover Block

Heading Block within a Cover Block

Rendered Block

Desktop (please complete the following information):

• OS: macOS 10.14.4
• Browser: Firefox Qunatum 66.0.5
• Version: WP 5.2.1