Dark purplish mucus in one-year-old, has anyone experienced this?

[Lalalalalax]

1 year old had dark purplish mucus in it this afternoon, has anyone experienced this? He has a slight sensitivity to diary but hasnt had anything with dairy in recently.

What has he had to eat or drink in the last couple of days?

Ive started keeping a diary since yesterday, sunday he had the same breakfast and a roast chicken dinner, i cant quite remember what he had for lunch.
The only new thing he has started to have is coconut milk and he has a banana everday.

Is there anything in that list that was a first time food?
If so, it might be worth making sure he doesn't have it for a week, then giving it again to see if there is a similar result.
A relative gave my toddler chocolate, followed by tomato juice (without my knowledge) and his nappies were terrible to behold, I was a bit worried until I asked what he had been given to eat.
Unless he seems to be unwell or in pain, it is worth just trying the food challenge test and see what happens.