Blue
Some months ago I learned that light blue was associated in the nineteenth century with the secret police, from a passage I found confusing in Leskov’s Laughter and Sorrow (Смех и горе, 1871). This is of course the sort of thing that turns out to have been everywhere all along once you know to look for it; here are some examples from the early chapters of Gertsen’s My Past and Thoughts (Былое и думы, 1852-68):
The greatly excited mental activity in Petersburg after Paul came to a grim close with December 14th. Nikolai appeared with his five gallows, hard labor, white strap, and light blue Benckendorff. (chapter 6)
Сильно возбужденная деятельность ума в Петербурге после Павла мрачно замкнулась 14 декабрем. Явился Николай с пятью виселицами, с каторжной работой, белым ремнем и голубым Бенкендорфом.
It was now our turn. Our names were already added to the secret police’s lists. The light blue cat’s first game with the mouse began thus. (chapter 6)
Черед был теперь за нами. Имена наши уже были занесены в списки тайной полиции. Первая игра голубой кошки с мышью началась так.
I was brought to a modest-sized office. The scribes, adjutants, officers – all was light blue. (chapter 11)
Меня привели в небольшую канцелярию. Писаря, адъютанты, офицеры – все было голубое.
“The legal code is intended for a different sort of crimes,” remarked the light blue colonel. (chapter 12)
– Свод законов назначен для преступлений другого рода, – заметил голубой полковник.
I was curious how translators would handle this, and it looks like Constance Garnett keeps “light blue” in each of these cases, sometimes making the reference to uniforms transparent (“the light blue uniform of Benckendorf,” “…were all in light blue”) and sometimes not (“the light-blue colonel”). Even though I just did the same thing myself, I wonder if it’s unnatural to keep that level of precision – the sentences might have more force if we just said “blue” in English instead of trying to keep up a distinction between голубой (light blue) and синий (dark blue).
XIX век 
Actually, it’s blue and indigo, so “light blue” is false precision. How did you interpret this before you knew that the secret police woer blue uniforms? Surely not throught the modern meaning of blue (gay)?
To me “indigo” seems like a word people memorize when they learn the official colors of the rainbow but few use, while “синий” to my non-native ear sounds like an entirely normal, non-technical word. If shown objects that Russians would consider голубые or синие, I think most English speakers would call them “blue,” “light blue,” or “dark blue,” depending.
I’d like to think that I’d have figured out the secret police connection if I’d noticed the My Past and Thoughts uses first, but in Leskov it was not quite so obvious, and even though I knew the “gay” meaning arose much, much later, it was hard not to let it interfere.
Here’s the Leskov quote: “[…] turning around, I saw, at the kind of dressing-table I was used to seeing in my mother’s bedroom… what can I call what I saw? I can put it no other way than that I saw Cupid in the flesh. I saw this and… was entirely at a loss, and with good reason. You remember, of course, that I was supposed to meet a captain here; but imagine my surprise when I saw at the dressing-table some blue creature [какое-то голубое существо] […] I just could not make up my mind whether it was a man or a woman.” This captain does work for the secret police, but that didn’t become clear to me until I read more of the story and eventually checked a footnote.