|Trillium grandiflorum population|
|Trillium grandiflorum - yes, T. grandiflorum, not T. grandiflorum f. roseum|
T. grandiflorum is a flower which changes colour as it ages. A pink flower like the above is just an older one, approaching its time of senescence. So when you see a pink individual (or a few pink individuals) among your T. grandiflorum population, just remember that it is more than likely just another T. grandiflorum that happens to be a bit older than the others.