Has anyone tested the forest alchemist?
Does it only change the color, or can it also change the markings?

I've used it a few times, and it usually just ends up changing a color into something common. Whenever I use it dragons, they just change back and forth between green, blue and red. So I presume that the chance of getting rarer colors is same as in the gene list: 2.22% for silver, etc.

Doesn't seem worth the high cost. But maybe I've just been unlucky with it?

It works on both color and pattern genes but changes to color seem far more common.

Heres the gene changes I've gotten so far:

Unicorn

• chestnut to white to gray
• buckskin to grey
• grey to chestnut to bay, buckskin to grey
• buckskin to black

Dragon

• piebald to normal to piebald
• striped to normal to piebald, normal to striped

Symurgh

• grey to red
• black to blue
• grey to blue
• brown to grey to red
• brown to grey

Cockatrice

• green to orange
• normal to piebald, blue to white

Roc

• brown to grey

Gryphon

• yellow/brown to piebald

Thank you!

I don't remember if I got anything good from them before I started logging my visits, but ever since then it's been nothing but common colors. I'll chalk that up to bad luck. 

Based on your results, it does seem to use the gene library percentages. So the chances of getting something like a silver dragon or white puma (1%) that way seem pretty slim...but still easier than trying to get one with mutagen.