Paul Christian sells seedlings of that variety in winter, he says you can tell from the colour of the leaves if the seedlings if the flowers are pink or white.
Have they flowered yet, and were they pink? From reading his description last year it sounded like his plants were unflowered with no guarantee of coour... I've unfortunately also read some discouraging remarks regarding size and quality from the other UK supplier, but I will probably give in to temptation in the end.
I'm still looking, so if there are anyone interested in selling me 1-3 bulbs of 'Roseum' (and/or other named Trillium grandiflorum), then please drop me a pm or an email!