Not to mention that, realistically, blood is a pretty damn dark red don’t you think?
View attachment 385634
The darker colored ones are mainly from veins while the brighter colored ones are from the arteries.
https://en.m.wikipedia.org/wiki/Blood
So unless the paint club actually has that dark of red and having it on your apron is quite common, it would be unrealistic to have students brush you off that quickly and not have any second thoughts as to why you have so much dark red stuff on your apron.
For reference, here’s what Yandere-Chan looks like when splattered with blood: