OMG OMG OMG!!!!! So friggin cute! Go for it, but if you have ANY doubts, don't. You need to be in LOVE with her as an adult whether she stays the same solor or turns purple
j/k about the purple....in all seriousness, she is a beautiful pup.
As long as you are 150% confident with the breeder and your personal love/want for your new fur baby, then go for it!
As far as how she will look as an adult it is SO hard to say. Sometimes they stay the exact same color and other times, they will "blow" their puppy coat to reveal a much lighter or darker color.
Just ask the breeder regarding her coloring, if they know her entire genetic history (which they should know numerous generations back if they are a reputable breeder) and they should be able to give you a fairly accurate assumption on her looks as an adult, keep us posted!
Are you also referring to her size as an adult?? If so, she looks like a larger Chi if she is only 4 weeks old (I am by no means an expert tho, I just have two Chis myself