I wouldn't mess with mh lamps since there's be a risk of explosion if something goes haywire.
Any high pressure lamp may explode, when something bad happens. It is true, for many MH's the regular wear was sufficient, but when thinking about e.g. ballast failure, any lamp may explode...
The HPS could reach blue part, when the arc is operating on high enough temperature (so current density), it is just the spectrum broadening reaching till the blue part. That way work the "white HPS" lamps...
But normally the HPS are not operated that high (it means lower efficacy, as the broadening happens towards IR as well and there it become part of losses)