The quality, manufacturing and the light characteristics of LED are evolving fast, what was an issue a few months ago might be a nonissue now.
But still, some LEDs are of bad quality and poorly powered, which is as important as the Diode itself.
I am using LED lights in my studio for about a year now, the Rosco's LitePad HO, these are built for photography and don't show any major issues, beside a faint green dominant which can be corrected with a 1/8 minus Green filter on the torch (see:
PHOTOEIL , the reproduction on the web is rather poor).
And be aware of monochromatic lights, particularly the LEDs, these are emitting a kind of over saturated, peaking narrow wave, light which is difficult to be handled by the post processing software (and some cameras).
Any light source that is deviating from the CIE CRI, the D5000 standard and has a colour dominant, can be considered as more or less monochromatic because a part of the (visual-) spectrum is cut away.
Read the very interesting postings by Ben-Edect!
It has all to do with budget, application, purpose and how they are built.