Thanks for the input everybody. Here’s what the DNR told me:
Thank you for contacting the MN DNR Info Center.
There is not a legal requirement for that, no. However, a well-hidden blind is also hidden from other hunters, so you might consider including some blaze for your own safety.
I’ll definitely add some orange if I hunt public lands, and probably go without on private land if I am the only hunter. Thanks again, Dave