Kibana 5.0 alpha 4 - where is color code for dark theme dashboard background please?

Anyone know where I can find the color for dark theme dashboard background in Kibana 5 please ?

I want to make some of a bar graph invisible by setting its color to the same as the background.

Many Thanks,

Mick

Here's where the color for the dark theme dashboard background is defined in Kibana 5: https://github.com/elastic/kibana/blob/2cf2218782d3c91e5a280baa2276eeb102621763/src/ui/public/styles/dark-variables.less#L58