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They grow best in sun but tolerate some shade, especially in warmer climates. Also, be sure to mulch them good to keep the soil cool for optimal growth. This article will help you with growing cauliflower: https://www.gardeningknowhow.com/edible/vegetables/cauliflower/growing-cauliflower.htm

Yes, it should be ok. This was either caused by the weather (some cauliflowers grow slightly purple under cooler or unusually hot conditions) or you could have bought a purple cauliflower (if you did not mean too, it was probably mislabled). Either way, it will not harm you. They are just as edible.

If you are getting plenty of flowers but nothing produces, then it is most likely due to poor pollination. Hand pollination often helps. These articles will help you with attracting more pollinators:
https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm
https://www.gardeningknowhow.com/garden-how-to/beneficial/creating-a-pollinator-garden.htm

If you are not seeing flowers, then you likely have too much nitrogen in the soil and should offset this by adding more phosphorus. This can be achieved by using a phosphorus-rich fertilizer or by adding bone meal.

There are several reasons your cauliflower may not be heading. Too much nitrogen can give you more foliage growth and little to no head formation. Adding more phosphorus can help with this. Your pH might be off--cauliflower likes a pH around 6.5. More imprtantly, they need cool weather in order to form heads. You can help keep them "cool" by placing mulch around the base of the plants.

This was either caused by the weather (some cauliflowers grow slightly purple under cooler or unusually hot conditions) or you could have bought a purple cauliflower (if you did not mean too, it was probably mislabled). Either way, it will not harm you. They are just as edible. This article will help with harvesting your cauliflower: https://www.gardeningknowhow.com/edible/vegetables/cauliflower/harvest-cauliflower.htm

It is not so much the time of year, but the heat of the year. In many parts of the country, it has been incredibly hot and even with mulching and watering well, the soil may just be too warm for the plants to form a head. I would not give up on them until they bolt. If they can get past this hot part of the summer without bolting, they may still form heads in the fall when it cools down.