We can select Maniphest priority colors using the `maniphest.priorities` config. As far as I can tell, we're limited to picking from just 10 colors (https://secure.phabricator.com/diffusion/P/browse/master/webroot/rsrc/css/phui/phui-object-item-list-view.css;e0bba9bae7f22edbac64790bb18b1b7575107d2e$387).
We currently have 7 different priorities, and we're finding that there's not enough variety within these 10 colors to easily distinguish all 7 priorities. For instance: indigo and violet look almost the same, and gray is used in many views to denote a closed task so we don't want to use that for any open ones.
We'd like to be able to use more colors, eg, the colors on this list: https://secure.phabricator.com/uiexample/view/PHUIColorPalletteExample/