The colors are different because the iris data doesn't include "cluster" as variable so your color scale's domain is invalid.

Your life would have been easier if you had just passed this function a g and attached the graph to the g rather than returning a distinct svg that then had to be incorporated into the master svg.

A loop would have been a far superior solution to listing out each sub graph individually.

JavaScript's template strings would be better than converting things to strings and appending them together. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals