Sin - more champagne-beige
Misty Mauve - most metallic looking, very reflective, lavender to mauve-y tone in different lighting
Blush - least reflective/metallic, almost matte, taupe-mauve color
Misty Mauve is not as tacky as sin, so you have to work quickly if you're using it as a primer to get your shadows to stick better. I would just use it as a cream shadow because it sets super quickly and doesn't crease. Also, once it's set, it doesn't allow powder shadows to cling to it, so it's really not a good primer. I guess it's called the "Essential Primer Eyeshadow" because it is an eyeshadow with primer built in. Not what I was expecting, but it is nice that it sets super well and lasts a long time. This product can also apply somewhat splotchy. You need to add a second layer of it to get decent pay off on the lids, but it still won't crease with two layers, so it's okay.
Sin is creamy, almost whipped in texture. It is the hardest to wash off, so it lasts the longest. It stays tacky so you can easily add shadows on top of it and make them really pop, but it's also not too creamy, it doesn't make your eyeshadow crease at all during the day.
Overall, the answer is no, neither of these ELF products are dupes for Urban Decay Sin Primer Potion.
Thanks for reading!