- backup original color style
sudo cp /usr/share/meld/styles/meld-base.xml /usr/share/meld/styles/meld-base.xml.backup
- replace base theme with dark theme
sudo cp /usr/share/meld/sytels/meld-dark.xml /usr/share/meld/styles/meld-base.xml
- replace style-scheme id "meld-dark" with "meld-base"
sudo vim /usr/share/meld/styles/meld-base.xml