How can I make a bluish "white" LED less blue?
Chromatic aberration interfering with reading would be a very unusual complaint (so says an ophthalmologist I know).  On the other hand, cataracts do block and scatter blue light more than the lower end of the visible spectrum.  So, if one has cataracts then it can be harder to read under blue light.  Most "white" LEDs use a monochromatic blue source (not UV), which is then fluoresced to the lower frequencies with phosphor.  Good phosphor is expensive, and more fluorescing hurts efficiency. Consequently, cheap LED sources tend to be blue and have a poor CRI.  Practically speaking, an LED with poor spectral characteristics cannot be improved once manufactured.  You need a different lamp.