I would love one of those.
I have an iPhone 5S, golden color. My husbandʻs hand-me-down.
The reason for my loving the concept of 5C: the colors!
I use the accessibility features heavily nowadays. VoiceOver, inverted colors, text-to-speech.... VoiceOver in several languages and with Braille input.
I only recently discovered that inverted colors accessibility setting is brilliant. When configured comfortably, there is a lot less visual clutter to me. And I can use my phone outdoors (Iʻve got the screen always on very dim, and if it needs adjustment, itʻs often via just VO as I canʻt see it. So typically I CANʻT USE MY PHONE OUTDOORS at all without VO).
Inverted colors is really odd: I can kind of see the pictures, but I canʻt tell the color anything, or e.g. "black" and "white" humans all look blue. But it helps make everything look cleaner - and helps me work better. No more writerʻs block. Itʻs just taking a lot of time and small adjustments to get everything to work optimally - since Iʻve been on OS X since 10.1...
5C looks like it had some of the color settings I love as a default option. Whereas with 5S I discovered what works for me accidentally. (After becoming fluent in VO for my own needs).
I would never complain of a phone or a shirt or shoe color looking ʻchildishʻ or ʻtoo girlyʻ for someone. Letʻs be more bold with colors.
I read braille, and I LOVE colors. I just canʻt rely on what a color is supposed to look like the way I use my Mac and iOS - hence also "differentiate without color". VoiceOver with OS X will still need a lot of learning...