It depends, look into your bulb. Like mentioned before, actinics sometimes are only for aesthetic purposes. There are some 10k bulbs out there that have plenty of 420nm, a 10k XM is a great example. Even though you dont see it, its still there. With that being said, there are plenty of blue bulbs out there (460nm) that offer little to no value to the zooxanthellae because they dont have any 420nm. Alot of t5 actinic bulbs are 460nm, there is only a few out there that peak at 420nm. In my opinion, you still cant beat URI VHO actinic.

A color that a bulb portrays can sometimes be misleading. Look into whatever bulb you are using, do some research on it and how much 420nm it puts out. You might be surprised with what you find, who know you might not even need supplimentation.

Blue light can make the color of some corals "pop" out. Make the greens a little greener or the blues a little bluer. If you dont use the right "blue" spectrum, no matter how blue your light is it wont turn that BROWN coral into anything, it will remain BROWN. However, if you use the right light (420nm) even though the light is whiter, that BROWN coral might turn into a beauty with a ton of color once the zooxanthellae start thriving.

For reference on lighting, google Sanjay