Seed stored for more than a year is probably dead. It's dust fine and should be surface sown since they require light for germination. Flowering begins in early May in my garden, starting with a short stalk topped by a cluster of buds, almost buried in the huge leaves. As the days pass, flowers open in a circle around the cluster of buds as the flower stalks lengthen. When one set of buds opens, another forms at the end of the flower stalk, extending the bloom period for a full month in my garden.
Colors vary considerably, ranging from white through pinks, reds, yellow and orange.
P. japonica species tend to be deep red with 'Miller's Crimson', a named form, said to be the finest. Postford White' has a conspicuous orange-yellow central ring, with somewhat paler foliage than the species. P. beesiana is rosy-carmine with a yellow eye, P. bulleyana is orange. Both of these were named for Mr. Bulley, founder of Bees' nursery in England, who was probably responsible for introducing more Asiatic Primula species than anyone else. I've seen photographs of mixed stands incorporating all the colors successfully, but my taste leans more toward the pinks and reds with a touch of blue rather than yellows and oranges.