I have acans under all sorts of different PAR readings. I have them at the 100-150 range, 180 and 260, but these are all different blue and white leaning lights. I have an acan bridge with 7 different colored colonies sitting under blue-dominant lights at around 150 PAR. These guys have only been under those lights for about a week, but they've been sitting under 200+ PAR for a month before then with no color shift. I'm excited to see which they prefer or react to.
A different rainbow acan under 250 lost some of its color on the main head, but the babies coming in seem to be used to the range, while the one sitting next to it retained its colors. There's so many variables, these wild and crazy acans. Easily my favorite coral.