Most LED's are not really picky bout the voltage they get, most 'standard' LED's will light up at about 1.5V (a common voltage used is 2V) more than 2.5 Volt will shorten its life span *edit*or KILL it.
But like I said not all LED's are created equal.
I think you're wondering if you can replace the regular LED's with blue ones, yes you can but AFAIK there are two types, one that uses 5V and one that uses 3.6V.
Most of the 3.6V types work fine at 2V or the voltage supplied by the mobo (I replaced the power LED with a blue one).
Hope that helped