Select an object, then select the “Line Style” tool from the toolbar.
Switching the Line Style setting from On to Off removes the line style from your object. You can add basic colors from the menu or create more custom colors using the color gradient. You can also use a hex code or swatch tool to more accurately match colors of other elements within your diagram.
You can also choose the line style (ex: dashed, dotted) from the Style drop-down menu.
Editor information before 6/27/18: https://support.cacoo.com/hc/en-us/articles/212778448-The-Editor