It's a complicated plant in that although it's usually a vigorous vine it can also be a shrub or a tree. Among other oddities, the leaves on the same plant can be different shapes. However, the flowers on one plant don't change colors regardless of the different leaf shapes. If the vine - or whatever - has one red flower then all the flowers on that plant (in that family) will be red.
Passion flowers range in color from red to pink to blue to purple to green to white to yellow....or a combination thereof. I've actually seen only a few but enjoy the ones I have come across - and I've enjoyed the photos of the ones I'll probably never come across. This one we grow at False Bluff. It's a vine with not only a beautiful flower but a delicious fruit:
Note: The link below is to an NIH study on the medicinal benefits of passiflora if you're so inclined. There are lots of studies, mostly small. I chose NIH because it's familiar...and that's important to some people.