I would think you’re racist, because it would clearly be in response to BLM and the idea of black liberation, not in response to hundreds of years of systemic dehumanization of white people. As GZA has pointed out, “context is critical.”
And, of course, you are avoiding the logic of my blue sky analogy. There are other things in the universe that are blue. Why does it not bother people to see a “The Sky Is Blue” shirt? There are other things in the universe that matter besides black lives. Why, then, do so many white people get butt-hurt about a “Black Lives Matter” shirt? Logically, these are equivalent. My theory is that said white people are racist. They either really don’t think black lives matter, or they won't acknowledge that systemic racism exists and that it is a problem. Neither shirt makes implications about anything other than the sky or black lives; if you make illogical inferences about them, that’s on you.