Inline Dropdown bg color in Gray 10 theme

[nelsonchen90]

What package(s) are you using?

• carbon-components
• carbon-components-react

Detailed description

Describe in detail the issue you're having.
Inline dropdown with Gray 10 theme applied, the background color is using $ui-background which is f4f4f4. But our designer is saying it should be white

Is this issue related to a specific component?
Yes, Dropdown

What did you expect to happen? What happened instead? What would you like to
see changed?
Our designer Marion Brülls says it should be white

What browser are you working in?
Chrome

What version of the Carbon Design System are you using?
v10

What offering/product do you work on? Any pressing ship or release dates we
should be aware of?
CP4D

Steps to reproduce the issue

https://ibm-analytics.slack.com/archives/C046Y0YUD/p1581450533133200