Theater people can be incredibly superstitious, but as far as I know nobody still respects dark days. Even the habit of not saying good luck is declining and people now wish both good luck and break a leg almost indiscriminately. Of course, some theaters and people are more superstitious than others, so there is no rule.
For example, even now, you will hardly hear somebody naming one certain Shakespeare’s play or wear purple the day of a performance. Superstitious gestures are also very common and in a place where I performed people would always form a circle together just before the curtain rised to cry out ‘shit’ three times in a row and proceed to slap each other’s butt as a way to bring good luck. Charming isn’t it?
Hope this helps!