[SpeedDial] SpeedDialAction visibility is poor on dark themes

[beverlycodes]

The icon and button colors on SpeedDialActions have weak visibility on dark themes. This can be seen on the material-ui site itself by switching to the dark theme and viewing the SpeedDial demo.

• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

SpeedDialAction should use a darker button color in themes where palette type is set to "dark".

Current Behavior

SpeedDialAction buttons are displayed with a white icon on a light background when palette type is set to "dark", making the icon difficult to see.

Steps to Reproduce (for bugs)

1. Go to https://material-ui.com/lab/speed-dial/
2. Click lightbulb in toolbar to switch to dark theme
3. Mouse over or click the SpeedDial button in either of the demos.
4. Notice that SpeedDialAction icons are difficult to see.

Context

Just experimenting with SpeedDial in my app and noticing that the action buttons are hard to differentiate on my app's dark theme.

Your Environment

Tech	Version
Material-UI	1.0.0-beta.38
React	16.2.0

[mbrookes]

@RyanFields You're quite right. Would you like to try and improve it?

[beverlycodes]

@mbrookes Started looking into a fix, but I need to spend time familiarizing myself with Material-UI's structure and inner workings. This is the first time I've tried working with the code. I will circle back to this in a couple weeks.

[mbrookes]

Thanks. Shout if you need any help. 📢

[onuraltun]

this issue is reproducing with same steps again