Design of line chart, pie chart and

We are building an online chart building app. I require a chart style to be designed that we can use as the default style.

People will be able to design their own charts but I want the default style to look great so that lots of people use it. Ideally, I would like people to know that a chart was built using our app just by looking at it.

There is no particular colour scheme to follow but I would like 2 or 3 chart types and they should all use the same set of colours.