I have a really simple trick for this, and I've used it to encourage "outside toys" vs "inside toys", "quiet toys" vs "loud toys", etc - even if my child really wanted only one type (and I wanted them to have the other for some reason). This also works for "stereotypical type A" vs "stereotypical type B", and it seems to work equally well with boys and girls.
Take a trip to the toy store/section with your child, letting them know they will get to pick out a toy! Depending on age, I usually add a price range restriction (under $10, under $20, etc).
Expect to spend a while and have fun, and encourage them to look at the variety of options. When they make a pick of the same class they usually do that I don't want them to limit themselves to (what a surprise, more Pokemon cards...), I say, "Well, you have a lot of toys like that one, don't you? Do you want a different type of toy?" If they are insistent (mine often are, as I think hardheadedness is genetically heritable...must get it from my father, right?), I pull out my secret weapon - "OK, I'll make you a deal - I'll buy you that toy, AND I'll buy you a second toy of a different kind!"
Then you take them to the different isle/section, and point them to the variety and let them pick from that set of toys. Now your child won't feel the need to cling to the one thing they want, sense they get to have it and they get a 'free' bonus toy for trying something new. Since they get to pick it out themselves, they'll be more likely to play with it.
I've used this technique successfully to get toys for a trip, toys for quiet time, toys that aren't guns/swords, toys that aren't more Pokemon cards, outside toys, books, you name it. The kid gets what they want, what they expected, and they get something extra - which is what you wanted the whole time.
You can then leave them to their own devices, and/or play with them and help them see new and different ways to have fun with all kinds of toys.
Bottom line, whatever you do, don't stress out over it - playing with barbies doesn't rob people of their ability to program or do math, nor does loving Star Wars give them the ability to be a software engineer (I have to remind myself this a lot, only with Monty Python). They are toys, they are supposed to be fun and help kids expand and improve their understanding of the world - and that can happen regardless of whether or not the toy is pink or camouflaged.
If your daughter ends up really loving one color, you might see if she'd like to paint other toys that color with you. If your child just loves yellow and there are no canary-yellow-sweater-wearing Storm Troopers, then we both know what you have to do.
Take a deep breath, and have a good time enjoying whatever toy your child picks. They'll likely start enjoying music you find god-awful soon enough, so enjoy these times while you can!