Answer: Flowers normally discolor as they age and, when spent, the petals naturally fall off the flower. I think what you are seeing is probably normal. It may have been speeded up a bit due to the stress of being transplanted, or if there were some extra cold nights, or if they were allowed to dry out, or if you used a water soluble fertilizer and it contacted the blooms.
Keep the soil evenly moist but not sopping wet or saturated. This helps the plants become rooted and bloom better faster. Do not over fertilize them. As the weather warms up these should grow and bloom better than early in the season.
Zinnias will bloom better if deadheaded regularly, which means snipping off the faded blooms. Vinca is usually self cleaning, meaning you do not need to deadhead. New flowers should be coming along to replace those that have faded.
Enjoy your flowers!
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