Perhaps I’m being a bit ‘nit picky’ but a few observations seem in order…
First, that photo is taken from above the buffalo, not at its same level. That’s why you can see his back over his horns and back feet higher than front feet. So all the shots, especially purple, will strike a bit lower than where it matters that you may think.
With the elevated location you’d be shooting from, say on a small hill above the buffalo, are you sure purple will reach the heart? Or might it go just under? Problem is, if you think you need to be a bit higher you’re shooting him in the mouth and that’s a really bad idea as
@steve white already mentioned. If you’re gonna brain him, is red high enough for the angle or would 1-2” higher be better?
Second, the buffalo is standing still, he’s not moving. So discussing shooting him in a charge is more theoretical than practical. Typically, when a buffalo facing you gets shot, he turns to run away. Unless already wounded he’s very unlikely to intentionally charge at the shot.
If I’m shooting at this target, I’m shooting just a bit above red. However, in real life I’m waiting for the buffalo to move before I shoot. Either raising his head to provide a better angle into the brain or heart, OR more likely to turn to depart and exposing his shoulder and heart/lung area from a much better angle. I know, I’m spoiling everyone’s fun but in real life he’s providing a more difficult target than on paper.
BTW, that buffalo is an absolute Tank!