As far as the orchid dottyback that you wanted... Look for the black
stripe on the eye. And the colored fins...

Why should I lokk for those features? Are those signs of health?

thanks for reply.....

Not signs of health; rather, distinguishing marks to help ensure you're
getting the correct fish. I've seen people buy the pseudochromis
instead of the dottyback because they look similar. And they get a
heck of a suprise in personality difference with these two fish. Best
of luck...