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If the parent plants were not orange and their seeds grow orange plants, then they were probably hybrids that revert back to orange when grown from seed. Some breeders develop the flowers this way to keep their variety exclusive. If you would like to grow marigolds from seed that stay multi-colored, you will need to find a multi-colored, non-hybrid variety and collect seeds from those plants.

It may be that some of the varieties you harvested were hybrids, which will not germinate. Bi-color marigolds especially tend to be hybrids. These need to be propagated by other methods.

This article will help with the earwigs: https://www.gardeningknowhow.com/plant-problems/pests/removing-earwigs-from-the-garden.htm

No, it will not affect the seeds. There are just a few plants overall that need distilled water and marigolds are not among them. Good luck with your project.

It is true that many insect pests, such as white flies, are put off by the smell of marigold plants. However, there are numerous pollinators (like bees) and predatory insects (like hover flies, which eat aphids) that are actually attracted to marigolds. Needless to say, it will not keep away important pollinators and may even attract other beneficial insects that feed on harmful ones.