Im just gonna add to the whole 'blood is paint' thing: paint has completely different
consistency than blood.
Most of the time you use more paint than water when painting with acrylics. Acrylics dont 'sink in' the clothing, because of their consistency, they stick to it. I also think your clothing gets slightly more stiff because of it. And most importantly, they dont come off if they dry, for years. Some artists get paid for painting with acrylics on peoples clothing because of that.
And if you did use a lot of water, then you wouldnt get this deep color on your clothing. Thats also why watercolors wouldnt work, since they are, surprise, based on water. And if you did somehow get splashed like that, SOMEHOW, watercolors are super easy to remove, just splash water on it. Running around like that would be unacceptable.
Dunno about the other types of paint, but I am almost sure they work similarly to acrylics.
Obviously it also depends on the type of material your clothes are made of, but it doesnt matter when youre asking if one could mistake blood for paint on someones clothing. Youd have to pay little attention to Ayano or be unable to smell the blood for this disguise to work.
Also, youd have to be a real goof or have a very weird style of painting to get splashed this much. Wouldnt it be weird if she 'had an accident' while painting everyday/every few days with that one specific color?