Yes, the white is the problem. You don't have to make it colorful, but try to give his skin atc at least a bit of color. You can use grey, cream white, blue white, or any other light, whiteish color. right now your knuffel looks like only lineart.
As for changes each stage should have at least 3 major changes. Right when you compare stage 1-2 you have one (in hair), stage 2-3 2 of them, 3-4 2 of them, 4-5 2 of them as well.
Some suggestions:
give him black panties in first stage and human ears
in second one make panties turn into long, black pants
add a new elements showing up in 3rd, 4th and 5th. Chest/ears/horn jewelery in gold would look nice maybe?
You could also give him regular human skin and hair color in first stages and then making him more pale in 3 or 4 stage, turning into white-ish/grey color in last stages.