Another thread was made about this like a week ago but I just experienced this myself last night.
So the enemy threw the marker, and as it landed the lines were red. About half a second after it landed the lines on the marker turned blue (the skyhammer was still standing there, he didn’t change teams) so I thought I’d stand there to see whether it actually damaged me or not and it did.
So it’s a visual bug, and no idea why it is happening, but yeah it seems from time to time enemy skyhammer markers show as blue.