[Lens] allow transparent "color" in color by value ramps

[ghudgins]

Describe the feature:
Transparent color option for color stops, hex values do not allow this

Describe a specific use case for the feature:
When I am in dark mode in Kibana
And I am visualizing a table in Lens with "Color by value" enabled
I need to set ramps where there is a "no color" stop in my color ramp
So I can have an option that works dynamically in dark or light mode without having to design my color stops for one or the other

Light mode works:

Dark mode doesn't:

CC @kmartastic

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[dej611]

@ghudgins it is possible to manually change the opacity for each color stop:

It is using a custom hex format made of 8 digits where the last 2 are for opacity.

[dej611]

Do you expect the default palettes to match the theme baseline color?

[ghudgins]

ooh - okay we can resolve this issue. The palette question is my next question but I think it's an EUI one. we should start monochromatic palette (maybe all of them or some of them like negative) from no color as it makes more sense to me.

For example, here is our default

[ghudgins]

@dej611 I think we still might have an issue with the text color logic

[dej611]

Can you open a separate issue for that?