The Fourth Doctor seems unduly alarmed the first time he meets Tegan. It's not until the Ninth Doctor era that the true reason is revealed: it was her clothes.
Danger! The Doctor twitched, catching at the edge of his vision an unexpected flash of mauve.
It was only Tegan. Tegan wore mauve.
When he knew she was there, it wasn't a problem. Mauve was lavender was violet was purple was only another color. He liked lilacs and orchids, liked grapes and aubergines. It was an innocent hue of nature in all its variations.
Labeling Tegan as trouble from the start simply because of the color of her airline uniform wasn't fair.
It was superstition.
So why did he feel better as she started doing without pieces of the uniform?