Ashley, Grace, and Tedd help Elliot demonstrate the differences in height between his many forms (by using clone forms in which only the hair and eye colors don't change).
Also, note to self, ask Ashley if she's ever considered a hairstyle like, because holy carp that's adorable.
Ellen COULD have helped with this, but she had a feeling that Ashley would love the excuse to transform into Elliot's default feminine form, so she claimed she had to go solve a mystery with Nanase.
Which wound up being true, but she didn't know it was going to be.
Tedd had very conflicted feelings about Grace in Elliot's form, and also wound up thinking about Elliot in Grace's form, which only made things worse for Tedd.
I wrote this as preview text for Tumblr, and decided I liked it enough to add to the commentary:
When you have multiple forms, the obvious solution to comparing the heights is to turn your friends into other versions of yourself. Obviously.
And keep their hair and eye colors the same so they're easy to identify. Obviously.
No, it has nothing to do with making the image more visually interesting, or seeing what someone might look like with purple hair. This is simply how you measure height.