Sorry, I shouldn't have said bigoted. I don't think it's a totally appropriate word here.
I can understand a bit that you feel like you're talking to a wall ( your MIL). I think we've all felt like what we're saying is falling on deaf ears some time or another, but this time it's just getting to you more because it's to do with DD.
From what I've read, it doesn't sound like she is doing this maliciously, so I would just accept the clothes with a thank you and put them away, obviously let her wear some of them if she wants.
I don't think anyone is in the wrong here. I don't think it would hurt for you to have a more open mind, and of course, as long as you continue to buy her clothes, she will always have the choice between neutral and pink. It's a touch unreasonable to think she should have to bear in mind pleasing you when she buys for her DGD.
However, if she never, ever buys anything remotely neutral and everything is the garish stereotype, it could be said that it's a little rude of her. Maybe not completely intentional but she may, of course, slightly resent not seeing her DGD dressed in pink all the time, in which case she is BU but probably realises that.
If its escalates then of course you could always mention it, but I don't think it should be blown up like that right now. It's just grandparents and their grandchildren, too many cooks and all that.
She's trying, and she could be a lot worse. I think it's important to remember that.
Sorry if I seemed harsh