Viola's first preorder will have five resin colors available: Pale Violet, Cream White, Pale Peach, Café au Lait, and Milk Chocolate.
These are my own color names that I'm using for some of Haru Casting's colors. The Haru color names, respectively, are: Pastel Violet, Cream White, Nanni Normal, Light Tan, and Cacao Tan. You might be able to find more resin color comparisons using the Haru names, but I haven't found many.
The only colors that I know match anything are the Cream White (which matches Unoa Fairy Skin) and Café au Lait (which is a ~75% match for Fairyland Tan and Unoa Paradise Skin). I'm not sure about any of the other colors. I don't have many dolls of my own, so I don't have a lot to compare.
Here are Cream White & Unoa Fairy Skin (top) and Café au Lait & Unoa Paradise Skin (bottom):
I also found a pretty good comparison of Haru Casting's Light Tan vs. Fairyland Tan >>here<<
I'm hoping to bring the resin samples to a doll meet very soon, so I can do more resin comparisons. I will update this post with more info when I do!
[Edit] Here are some sample comparisons from the meet! Specifically, the Fairyland resin comparisons since those are what I get asked the most about. Thanks to IG @salem_sisterhood for the photos!
Summerbird Pale Peach (Haru Nanni Normal) vs. Fairyland Normal
Summerbird Café au Lait (Haru Light Tan) vs. Fairyland Tan
Summerbird Cream White (Haru Cream White) vs. Fairyland White
I hope these comparisons will be helpful for you if you're planning on making a hybrid!