Are your previously solid color pink or rose colored lily flowers beginning to show random streaking of white on the petals? Although it can be quite pretty, the cause is usually viral based, but in some cases can also be weather related early in the season if the white coloration is showing up only on the earliest leaves. Remember the old "Rembrandt" tulips of years past? The cause was due to "Tulip Color Breaking Virus" which caused wild strips of differing colors. The similar "Tobacco Mosaic Virus" can be transferred to lilies from touching flowers or stems while using chewing tobacco or by dropping spent butts on the ground in the lily garden.
Plants "catch" a virus similar to the way we fall victim to a head cold or influenza. Sucking insects, such as aphids, can transfer virus diseases from plant to plant and should be controlled in the garden. All garden-grown plants, whether lily, iris, dahlia, Rose or tulip have one or more viruses present in the tissues. Trouble doesn't start until several different viruses find a home in the same plant. A plant can grow quite happily with one or two different strains of virus, but will begin to show streaking and twisting in the leaves, and eventual death, if several more strains are added. This is similar to an office worker functioning with a simple head cold, but add the flu as well, and it suddenly becomes hard to function.
There is no cure for plant viruses, only prevention. Regularly inspect your garden throughout the growing season, bearing in mind that some cultivars may have suspicious-looking foliage early in the season, but look great later. This is due to environment, not virus. If in a group of recently planted lilies, all look great except one, keep an eye on the one which looks unhealthy, but check for outside factors, such as mechanical damage to the sprout, insect activity, or competition from overly aggressive trees, shrubs or ground covers. It is best to control aphids, and wait until early the next season before passing judgment. Relocating bulbs to better drained soil, adding humus, or providing Trace Elements will many times correct foliage concerns.
Note: The old-fashioned Tiger Lily (Lilium tigrinum); tall, orange re-curved flowers is heavily infected with viruses, do not plant with other lilies, keep isolated by at least 100 feet to be safe.