What causes the difference in the color of blood

Oxygenated (arterial) blood is bright red, while dexoygenated (venous) blood is dark reddish-purple. The difference is color results from the electronic state of the iron ion (ferrous vs ferric), which in turn influences the π → π* and n → π* electronic transitions of porphyrin and hence its optical characteristics.

Pigment molecules binding to oxygen molecules.

nope, but i have cleaned my brush in my cup of not as potentially harmful but nevertheless, very upsetting for scottish/british folks. especially if you've used the last teabag for it

explanation:

there could be something in that . . i am indeed an old scottish man!

there's a bit of bolshie-ness with it too though. i won't let go of the old ways . . tea and whisky . . whether the young whippersnappers like it or not!