Sorry, but I can't agree with this one either :p 
It's inconsistent with the Vec4 class which puts red into the MSB. What's wrong with changing the code 
u8 r = (src>>12) & 0x0F;
u8 g = (src>>8) & 0x0F;
u8 b = (src>>4) & 0x0F;
u8 a = src & 0x0F;
?