Two main ways. First is they inject them with dye. The second is more common, an acid bath to strip them of their slime coat and then dipped in dye then repeat.
Now that is absolute animal cruelty, the animal right groups have a huge fuss when we cut dog tails off but not fish tails! Fish practically need those to live. This is absolute animal cruelty!
Here is a pic of the Strawberry. I you most of you are right. After I got it is when I realized its a dyed fish. I couldnt find anything on line about them.
I figure the color will fade, but if it grows and looks anything like my other Silver Aro then I am fine with that. My bigger Silver has a beautiful orange tint to it on the fins.