I'm assuming you mean Nandina domestica 'Firepower', right? The red color comes out on mature foliage as the days become shorter, and will be much brighter in more light. It fades in the spring but doesn't ever go back to all green.

The new emerging growth will be lime green then tinged with faded yellows and oranges.

It's my least favorite of all nandina, for some reason. Always looks sick to me, lol.

i cant tell you how many baby yellowish conifers i thought were sickly yellow.. for years. . chlorotic ... and dying ... until they put on enough size to look good.. lol ...

dont forget.. if your shade is deciduous trees .. your sun levels will go up.. once those leaves fall .. so its an added variable ...

color change in fall is never exactly predictable ... because so many variables impact such ... so it would be very hard for anyone to tell you.. how its will all time out in your yard ... one trick i have for predicting such.. is to just learn to ID it as you drive the area ... and see when others are doing their thing ...

ken