This is my color preset in Sketch app. It's perfect for all those super grayscale Sketch fantasies you have.
You can grab it if you like.
Copy and paste the following commands into Terminal and press return to run.
cd ~/Library/Containers/com.bohemiancoding.sketch3/Data/Library/Application\ Support/com.bohemiancoding.sketch3/
mv assets-v55.sketchpreset assets-v55.sketchpreset.backup
curl -O https://github.com/danieljacobarcher/my-sketch-colors/raw/master/assets-v55.sketchpreset
echo "All Done! Now restart Sketch app."
cd ~/Library/Application Support/com.bohemiancoding.sketch3/
mv assets-v55.sketchpreset assets-v55.sketchpreset.backup
curl -O https://github.com/danieljacobarcher/my-sketch-colors/raw/master/assets-v55.sketchpreset
echo "All Done! Now restart Sketch app."
You can also restore your colors if you regret it.
If you got any better ideas, Just send me a pull request or add an issue.
This is provided as-is. I will not be providing support, at all. Maybe call Mr. Grey.