Pregnancy risk on glow

Beena
So I noticed on this app, after my period; the high risk days are red-so two days after my period it's 9% HIGH risk, and normally, the purple days are just 7.6% risk. 
So is it really NOT a good idea to have sex on those red days? Or is it just..I mean; what's the diff between 7.6% risk and 9% HIGH risk?