Hi everyone! 
Thanks for this useful cohort plot! It seems really nice, but there are some small issues.
One issue with the cohort plot, is that it always provides percentages i.e. it has always to compare two values and get a percentage. While this is useful, it does not offer the capability to extend this, by showing additional numeric values. e.g. if you want to see user activity by sign-up date on monthly basis, you don’t necessarily want to see the percentage of the users that meet a criterion, but maybe if you are amazon, the average amount of money each user spent that month.
One additional issue has to do with colouring the plot. Plots are shown only with shades of blue. I did not find a way in the UI to change this colour to red, orange etc. Also, since it always shows percentages, it automatically associates values close to 100% to dark blue and values close to 0% to light blue. While this intuitively is correct, one might want to observe slight variations. e.g. in the previous example of user activity by sign-up date on monthly basis, you might have 30-40% of the users coming back each month to your website. So values near 30% should be set to light blue and values near 40% should be set to dark blue. In the current version, they all get roughly the same colour.
Are those changes scheduled to be done at some point?